U.S. patent number RE33,683 [Application Number 07/357,249] was granted by the patent office on 1991-09-03 for catalyst composition for polymerizing alpha-olefins.
This patent grant is currently assigned to Mobil Oil Corporation. Invention is credited to Louanne M. Allen, Robert O. Hagerty, Richard O. Mohring.
United States Patent |
RE33,683 |
Allen , et al. |
* September 3, 1991 |
Catalyst composition for polymerizing alpha-olefins
Abstract
A catalyst composition for polymerizing alpha-olefins is
prepared by reacting a transition metal compound, e.g., titanium,
with trimethylaluminum catalyst activator. In a preferred
embodiment, the catalyst is supported on a porous refractory
support and is prepared by additionally reacting a magnesium
compound or an organomagnesium composition with the support. Also
disclosed is a process for polymerizing alpha-olefins in the
presence of the catalyst of the invention. The polymer products
have higher bulk density and produce films of greater strength than
polymers prepared with similar catalysts utilizing different
alkyl-aluminum activators, e.g., triethylaluminum and
triisobutylaluminum.
Inventors: |
Allen; Louanne M. (Port Arthur,
TX), Hagerty; Robert O. (Metuchen, NJ), Mohring; Richard
O. (Sour Lake, TX) |
Assignee: |
Mobil Oil Corporation (Fairfax,
VA)
|
[*] Notice: |
The portion of the term of this patent
subsequent to March 22, 2005 has been disclaimed. |
Family
ID: |
26999575 |
Appl.
No.: |
07/357,249 |
Filed: |
May 26, 1989 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
822359 |
Jan 24, 1986 |
04732882 |
Mar 22, 1988 |
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Current U.S.
Class: |
502/107; 502/103;
502/120; 502/132; 502/112; 502/104; 502/115; 502/126; 502/134;
526/129 |
Current CPC
Class: |
C08F
210/02 (20130101); C08F 210/02 (20130101); C08F
4/6425 (20130101) |
Current International
Class: |
C08F
210/02 (20060101); C08F 210/00 (20060101); C08F
004/645 () |
Field of
Search: |
;502/103,104,112,115,120,126,132,134,107 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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120503 |
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Oct 1984 |
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EP |
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1065616 |
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Sep 1956 |
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DE |
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1056616 |
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Jan 1958 |
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DE |
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52-122079 |
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Nov 1977 |
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JP |
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Other References
Allen et al., U.S. patent application Ser. No. 037,680, filed
04/13/87..
|
Primary Examiner: Garvin; Patrick P.
Attorney, Agent or Firm: McKillop; A. J. Speciale; C. J.
Schneller; M. V.
Claims
We claim:
1. In a process for preparing an alpha-olefin polymerization
catalyst composition .Iadd.for polymerizing ethylene and at least
one C.sub.3 -C.sub.10 alpha-olefin to produce a linear low density
copolymer having a density of about 0.940 gm/cc or less,
.Iaddend.comprising, .Iadd.a precursor composition which comprises
.Iaddend.a .Iadd.halogen-containing .Iaddend.transition metal
compound .Iadd.and .Iaddend.a magnesium compound.Iadd., which
precursor composition is supported on a solid, porous carrier,
.Iaddend.and a metal alkyl .Iadd.activator, .Iaddend.the
improvement comprising using trimethylaluminum as the metal alkyl
.Iadd.activator.Iaddend..
2. A process of claim 1 wherein the magnesium compound is an
organomagnesium composition.
3. A process of claim 2 wherein the catalyst composition is
prepared by:
(A) contacting a solid, porous carrier with the organomagnesium
composition;
(B) contacting the product of step (A) with the transition metal
compound; and
(C) contacting the product of step (B) with the
trimethylaluminum.
4. A process of claim 3 wherein the catalyst composition is
prepared in a process comprising the steps of:
(i) contacting a solid, porous carrier having reactive OH groups
with a liquid containing at least one organomagnesium composition
having the empirical formula:
where R and R' are the same or different and they are C.sub.1
-C.sub.12 hydrocarbyl groups, provided that R' may also be a
halogen, and n is 0, 1 or 2, the number of moles of said
organomagnesium composition being in excess of the number of moles
of said OH groups on said carrier;
(ii) evaporating said liquid from step (i) to produce a supported
magnesium composition in the form of a dry, free-flowing powder;
and
(iii) reacting said powder of step (ii) with at least one
transition metal compound in a liquid medium, the number of moles
of said transition metal compound being in excess of the number of
moles of the OH groups on said carrier prior to the reaction of the
carrier with said organomagnesium composition in step (i), said
transition metal compound being soluble in said liquid medium, and
said supported magnesium composition being substantially insoluble
in said liquid medium.
5. A process of claim 4 wherein the transition metal compound is a
titanium compound.
6. A process of claim 5 wherein the titanium compound is a
tetravalent titanium compound.
7. A process of claim 6 wherein the catalyst composition comprises
such an amount of the trimethylaluminum that the polymer prepared
with the catalyst composition comprises about 15 to about 300 parts
per million of the trimethylaluminum.
8. A process of claim 7 wherein n is 1.
9. A process of claim 8 wherein said step (i) comprises:
(a) slurrying the carrier in a non-Lewis base liquid; and
(b) adding to the slurry resulting from step (a) the
organomagnesium composition in the form of an ether solution
thereof.
10. A process of claim 9 wherein the ether is tetrahydrofuran.
11. A process of claim 10 wherein the porous, solid carrier is
silica, alumina or combinations thereof.
12. A process of claim 11 wherein the porous, solid carrier is
silica.
13. A process of claim 12 wherein the tetravalent titanium compound
is TiCl.sub.4.
14. A process of claim 13 wherein, in step (i), the ratio of the
number of moles of said organomagnesium composition to the number
of moles of the OH groups on said silica is from about 1.1 to about
3.5.
15. A process of claim 14 wherein in step (i), the ratio of the
number of moles of said organomagnesium composition to the number
of moles of the OH groups on said silica is about 1.5 to 3.5.
16. A process of claim 15 wherein said liquid medium is an alkane,
cycloalkane, aromatics or halogenated aromatics.
17. A process of claim 16 wherein said liquid medium is hexane.
18. A process of claim .[.17.]. .Iadd.58 .Iaddend.wherein, prior to
contacting the silica in step (i), it is heated at a temperature of
about 750.degree. C. for at least four hours.
19. A process of claim 18 wherein the organomagnesium composition
is ethylmagnesium chloride.
20. In a alpha-olefin polymerization catalyst composition.[.,.].
.Iadd.used to polymerize ethylene and at least one C.sub.3
-C.sub.10 alpha-olefin to produce a linear low density copolymer
having a density of about 0.940 gm/cc or less, .Iaddend.comprising
.Iadd.a precursor composition which comprises .Iaddend.a
.Iadd.halogen-containing .Iaddend.transition metal compound.[.,.].
and a magnesium compound.Iadd., which precursor composition is
supported on a solid, porous carrier, .Iaddend.and a metal alkyl
activator, the improvement comprising using trimethylaluminum as
the metal alkyl .Iadd.activator.Iaddend..
21. A catalyst composition of claim 20 wherein the magnesium
compound is an organomagnesium composition.
22. A catalyst composition of claim 21 wherein it is prepared
by:
(A) contacting a solid, porous carrier with the organomagnesium
composition;
(B) contacting the product of step (A) with the transition metal
compound; and
(C) contacting the product of step (B) with the
trimethylaluminum.
23. A catalyst composition of claim 22 wherein it is prepared in a
process comprising the steps of
(i) contacting a solid, porous carrier having reactive OH groups
with a liquid containing at least one organomagnesium composition
having the empirical formula:
where R and R' are the same or different and they are C.sub.1
-C.sub.12 hydrocarbyl groups, provided that R' may also be a
halogen, and n is 0, 1 or 2, the number of moles of said
organomagnesium composition being in excess of the number of moles
of said OH groups on said carrier;
(ii) evaporating said liquid from step (i) to produce a supported
magnesium composition in the form of a dry, free-flowing powder;
and
(iii) reacting said powder of step (ii) with at least one
transition metal compound in a liquid medium, the number of moles
of said transition metal compound being in excess of the number of
moles of the OH groups on said carrier prior to the reaction of the
carrier with said organomagnesium composition in step (i), said
transition metal compound being soluble in said liquid medium, and
said supported magnesium composition being substantially insoluble
in said liquid medium.
24. A catalyst composition of claim 23 wherein the transition metal
compound is a titanium compound.
25. A catalyst composition of claim 24 wherein the titanium
compound is a tetravalent titanium compound.
26. A catalyst composition of claim 25 which comprises such an
amount of the trimethylaluminum that the polymer prepared with the
catalyst composition comprises about 15 to about 300 parts per
million of the trimethylaluminum.
27. A catalyst composition of claim 26 wherein n is 1.
28. A catalyst composition of claim 27 wherein said step (i)
comprises:
(a) slurrying the carrier in a non-Lewis base liquid; and
(b) adding to the slurry resulting from step (a) the
organomagnesium composition in the form of an ether solution
thereof.
29. A catalyst composition of claim 28 wherein the ether is
tetrahydrofuran.
30. A catalyst composition of claim 29 wherein the porous, solid
carrier is silica, alumina or combinations thereof.
31. A catalyst composition of claim 30 wherein the porous, solid
carrier is silica.
32. A catalyst composition of claim 31 wherein the tetravalent
titanium compound is TiCl.sub.4.
33. A catalyst composition of claim 32 wherein, in step (i), the
ratio of the number of moles of said organomagnesium composition to
the number of moles of the OH groups on said silica is from about
1.1 to about 3.5.
34. A catalyst composition of claim 33 wherein, in step (i), the
ratio of the number of moles of said organomagnesium composition to
the number of moles of the OH groups on said silica is about 1.5 to
3.5.
35. A catalyst composition of claim 34 wherein said liquid medium
is an alkane, cycloalkane, aromatics or halogenated aromatics.
36. A catalyst composition of claim 35 wherein said liquid medium
is hexane.
37. A catalyst composition of claim .[.36.]. .Iadd.60
.Iaddend.wherein, prior to contacting the silica in step (i), it is
heated at a temperature of about 750.degree. C. for at least four
hours.
38. A catalyst composition of claim 37 wherein the organomagnesium
composition is ethylmagnesium chloride.
39. A process of claim 1 wherein the catalyst composition is
prepared by
(A) contacting a solution of a magnesium compound in a liquid with
a titanium compound;
(B) contacting the resulting solution of step (A) with a solid,
inert porous carrier to form a catalyst precursor; and
(C) contacting the precursor with the trimethylaluminum.
40. A process of claim 39 wherein the magnesium compound has the
empirical formula
wherein X is Cl, Br, I or mixtures thereof.
41. A process of claim 40 wherein the magnesium compound is
MgCl.sub.2.
42. A process of claim 41 wherein said liquid is at least one Lewis
base.
43. A process of claim 42 wherein the Lewis base is selected from
the group consisting of aliphatic carboxylic acids, aromatic
carboxylic acids, aliphatic ethers, cyclic ethers and aliphatic
ketones.
44. A process of claim 43 wherein the Lewis base is selected from
the group consisting of aliphatic ethers and cyclic ethers.
45. A process of claim 44 wherein the Lewis base is
tetrahydrofuran.
46. A process of claim 45 wherein the titanium compound is
TiCl.sub.3, TiCl.sub.4, Ti(OCH.sub.3)Cl.sub.3, Ti(OC.sub.6
H.sub.5)Cl.sub.3, Ti(OCOCH.sub.3)Cl.sub.3 to Ti(OCOC.sub.6
H.sub.5)Cl.sub.3.
47. A process of claim 46 wherein the titanium compound is
TiCl.sub.3.
48. A catalyst composition of claim 20 wherein it is prepared
by
(A) contacting a solution of a magnesium compound in a liquid with
a titanium compound;
(B) contacting the resulting solution of step (A) with a solid,
inert porous carrier to form a catalyst precursor, and,
(C) contacting the precursor with the trimethylaluminum.
49. A catalyst composition of claim 48 wherein the magnesium
compound has the empirical formula
wherein X is Cl, Br, I or mixtures thereof.
50. A catalyst composition of claim 49 wherein the magnesium
compound is MgCl.sub.2.
51. A catalyst composition of claim 50 wherein the liquid is at
least one Lewis base.
52. A catalyst composition of claim 51 wherein the Lewis base is
selected from the group consisting of aliphatic carboxylic acids,
aromatic carboxylic acids, aliphatic ethers, cyclic ethers and
aliphatic ketones.
53. A catalyst composition of claim 52 wherein the Lewis base is
selected from the group consisting of aliphatic ethers and cyclic
ethers.
54. A catalyst composition of claim 53 wherein the Lewis base is
tetrahydrofuran.
55. A catalyst composition of claim 54 wherein the titanium
compound is TiCl.sub.3, TiCl.sub.4, Ti(OCH.sub.3)Cl.sub.3,
Ti(OC.sub.6 H.sub.5)Cl.sub.3, Ti(OCOCH.sub.3)Cl.sub.3 or
Ti(OCOC.sub.6 H.sub.5)Cl.sub.3.
56. A catalyst composition of claim 55 wherein the titanium
compound is TiCl.sub.3. .Iadd.
57. A process of claim 17 wherein the silica, prior to the
contacting thereof in said step (i), is heated at a temperature of
about 750.degree. to about 850.degree. C. for 16 hours or less.
.Iaddend. .Iadd.58. A process of claim 57 wherein the
organomagnesium composition R' is Cl, Br or I. .Iaddend. .Iadd.59.
A catalyst composition of claim 36 wherein the silica, prior to the
contacting thereof in said step (i), is heated at a temperature of
about 750.degree. to about 850.degree. C. for 16 hours or less.
.Iaddend. .Iadd.60. A catalyst composition of claim 59 wherein in
the organomagnesium composition R' is Cl, Br or I.
Description
This application is a reissue of Ser. No. 822,359, filed Jan. 24,
1986 and issued Mar. 22, 1988 as U.S. Pat. No. 4,732,882.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a catalyst for polymerizing
alphaolefins, a method for producing such a catalyst and to a
method of polymerizing alpha-olefins with such a catalyst. A
particular aspect of the present invention relates to a method for
preparing a high activity catalyst composition which produces
medium density and linear low density polyethylene (LLDPE), having
relatively narrow molecular weight distribution, and to the
polymerization process utilizing such a catalyst composition.
2. Description of the Prior Art
Linear low density polyethylene polymers possess properties which
distinguish them from other polyethylene polymers, such as ethylene
homopolymers. Certain of these properties are described by Anderson
et al, U.S. Pat. No. 4,076,698.
Karol et al, U.S. Pat. No. 4,302,566, describe a process for
producing certain linear low density polyethylene polymers in a gas
phase, fluid red reactor.
Graff, U.S. Pat. No. 4,173,547, Stevens et al, U.S. Pat. No.
3,787,384, Strobel et al, U.S. Pat. No. 4,148,754, and Ziegler,
deceased, et al, U.S. Pat. No. 4,063,009, each describe various
polymerization processes suitable for producing forms of
polyethylene other than linear low density polyethylene, per
se.
Graff, U.S. Pat. No. 4,173,547, describes a supported catalyst
obtained by treating a support with both an organoaluminum compound
and an organomagnesium compound followed by contacting this treated
support with a tetravalent titanium compound.
Stevens et al, U.S. Pat. No. 3,787,384, and Stroebel et al, U.S.
Pat. No. 4,148,754, describe a catalyst prepared by first reacting
a support (e.g., silica containing reactive hydroxyl groups) with
an organomagnesium compound (e.g., a Grignard reagent) and then
combining this reacted support with a tetravalent titanium
compound. According to the teachings of both of these patents, no
unreacted organomagnesium compound is present when the reacted
support is contacted with the tetravalent titanium compound.
Ziegler, deceased, et al, U.S. Pat. No. 4,063,009, describe a
catalyst which is the reaction product of an organomagnesium
compound (e.g., an alkylmagnesium halide) with a tetravalent
titanium compound. The reaction of the organomagnesium compound
with the tetravalent titanium compound takes place in the absence
of a support material.
A vanadium-containing catalyst, used in conjunction with
triisobutylaluminum as a co-catalyst, is disclosed by W. L. Carrick
et al in Journal of American Chemical Society, Volume 82, page 1502
(1960) and Volume 83, page 2654 (1961).
Nowlin et al, U.S. Pat. No. 4,481,301, the entire contents of which
are incorporated herein by reference, disclose a supported
alpha-olefin polymerization catalyst composition prepared by
reacting a support containing OH groups with a stoichiometric
excess of an organomagnesium composition, with respect to the OH
groups content, and then reacting the product with a tetravalent
titanium compound. The thus-obtained catalyst is activated with a
suitable activator, e.g., disclosed by Stevens et al, U.S. Pat. No.
3,787,384 or by Stroebel et al, U.S. Pat. No. 4,148,754. The
preferred activator of Nowlin et al is triethylaluminum.
It is primary object of the present invention to prepare a catalyst
composition for the polymerization of alpha-olefins which yields
polymerization products having a relatively narrow molecular weight
distribution.
Additional objects of the present invention will become apparent to
those skilled in the art from the following description.
SUMMARY OF THE INVENTION
An alpha-olefin polymerization catalyst composition is prepared in
a process comprising reacting a transition metal compound with
trimethylaluminum, used as the catalyst activator.
In one preferred embodiment, the catalyst composition is prepared
in a process comprising contacting an organomagnesium composition
with a solid, porous carrier and contacting the product of that
step with a transition metal compound, as described by Nowlin et
al, U.S. Pat. No. 4,481,301. The resulting precursor product is
then contacted with trimethylaluminum.
In another preferred embodiment, the catalyst composition is
prepared in a process comprising forming a precursor composition
from a magnesium compound, a titanium compound and an electron
donor compound and diluting the precursor composition with an inert
carrier, as described by Karol et al, European Patent Application
No. 8410344.6, filed Mar. 28, 1984, Publication No. 0 120 503,
published on Oct. 3, 1984, the entire contents of which are
incorporated herein by reference. The precursor is then activated,
in accordance with the present invention, with
trimethylaluminum.
The invention is also directed to an alpha-olefin polymerization
process conducted in the presence of a catalyst composition of this
invention and to the polymer products produced thereby.
BRIEF DESCRIPTION OF THE FIGURE
The FIGURE is a graphical representation of the effect of TMA
content on productivity for the catalyst of Examples 5-9.
DETAILED DESCRIPTION OF THE INVENTION
We unexpectedly found that the use of trimethylaluminum (TMA) as
the activator for the precursor composition instead of
triethylaluminum (TEAL), commonly used heretofore as the preferred
catalyst activator, produces improved catalyst compositions which,
when used in alpha-olefin polymerization reactions, produce linear
low density polyethylene polymer resins (LLDPE) and high density
resins having substantially lower values of melt flow ratio (MFR)
(calculated by dividing the value of high load melt index, HLMI,
I.sub.21, by the value of melt index, MI, I.sub.2, for a given
polymer) than similar resins produced with similar catalyst
compositions synthesized with TEAL as the catalyst activator.
Additionally, the polymer resins produced with the novel catalyst
composition of this invention have reduced hexane extractables, and
films manufactured from such polymer resins have improved strength
properties, as compared to resins and films prepared from resins
made with catalyst compositions activated with TEAL.
The resins prepared with the catalyst of the invention may have
higher settled bulk densities than the resins prepared with similar
catalysts synthesized with TEAL or other prior art activators, and
may have substantially improved higher alpha-olefins, e.g.,
1-hexane, incorporation properties, as compared to similar catalyst
compositions synthesized with triethylaluminum. The improvements of
the present invention are unexpected, especially since other
workers in this field have emphasized the use of TEAL as the
preferred catalyst activator (e.g., see Nowlin et al, U.S. Pat. No.
4,481,301).
The term "hexane extractables" is used herein to define the amount
of a polymer sample extracted by refluxing the sample in hexane in
accordance with the FDA-approved procedure. As is known to those
skilled in the art, the FDA requires that all polymer products
having food contact contain less than 5.5% by weight of such hexane
extractables.
The polymers prepared in the presence of the catalyst of this
invention are linear low density polyethylene resins or high
density polyethylene resins which are homopolymers of ethylene or
copolymers of ethylene and higher alpha-olefins. They exhibit
relatively low values of melt flow ratio, evidencing a relatively
narrow molecular weight distribution, than similar polymers
prepared in the presence of similar previously-known catalyst
compositions prepared with TEAL as the activator, e.g., those
disclosed by Karol et al, European Patent Application No.
84103441.6. Thus, the polymers prepared with the catalysts of this
invention are especially suitable for the production of low
density, high strength film resins, and low density injection
molding resins.
The manner of combining the TMA catalyst activator with the
catalyst precursor is not critical to the present invention, and
the TMA may be combined with the precursor in any convenient, known
manner. Thus, the TMA may be combined with the catalyst precursor
either outside of the reactor vessel, prior to the polymerization
reaction, or it can be introduced into the reactor vessel
simultaneously or substantially simultaneously with the catalyst
precursor.
The catalyst precursor (defined herein as the catalyst composition
prior to the reaction thereof with the trimethylaluminum, TMA) is
any one of the well known to those skilled in the art Ziegler
catalyst precursors comprising a transition metal or a compound
thereof, e.g., titanium tetrachloride. The catalyst precursor may
be supported on an insert support, e.g., see Karol et al, U.S. Pat.
No. 4,302,566 and Newlin et al, U.S. Pat. No. 4,481,301, or
unsupported, e.g., Yamaguchi et al, U.S. Pat. No. 3,989,881.
Suitable catalyst precursor compositions are disclosed, for
example, by Yamaguchi et al, U.S. Pat. No. 3,989,881; Nowlin et al,
U.S. Pat. No. 4,481,301; Hagerty et al, U.S. Pat. No. 4,562,169;
Goeke et al, U.S. Pat. No. 4,354,009; Karol et al, U.S. Pat. No.
4,302,566; Strobel et al, U.S. Pat. No. 4,148,754; and Ziegler,
Deceased, et al, U.S. Pat. No. 4,063,009, the entire contents of
all of which are incorporated herein by reference.
Catalyst compositions produced in accordance with the present
invention are described below in terms of the manner in which they
are synthesized.
Any one or a combination of any of the well known transition metal
compounds can be used in preparing the catalyst precursor of this
invention. Suitable transition metal compounds are compounds of
Groups IVA, VA, or VIA, VILA or VIII of the Periodic Chart of the
Elements, published by the Fisher Scientific Company, Catalog No.
5-702-10, 1978, e.g., compounds of titanium (Ti), zirconium (Zr),
vanadium (V), tantalum (Ta), chromium (Cr) and molybdenum (Mo),
such as TiCl.sub.4, TiCl.sub.3, VCl.sub.4, VCl.sub.3, VOCl.sub.3,
MoCl.sub.5, ZrCl.sub.5 and chromiumacetylacetonate. Of these
compounds, the compounds of titanium and vanadium are preferred,
and the compounds of titanium are most preferred. The transition
metal compound is reacted with TMA in any conventional manner in
which the transition metal compounds of prior art were reacted with
the activators used in prior art. For example, the transition metal
compound can be dissolved in a suitable solvent, e.g., isopentane
or hexane, and the resulting solution reacted with TMA, which may
also be used as a solution in a suitable solvent, e.g., isopentane.
It is preferable, however to introduce the catalyst precursor into
a reactor and introduce the TMA activator into the reactor
simultaneously with the introduction of the catalyst precursor or
after the introduction of the precursor is terminated.
In an alternative and preferred embodiment, the catalyst precursor
composition is prepared by reacting an organometallic or a halide
compound of Groups IA to IIIA with a transition metal compound. The
Group IA to IIIA organometallic or halide compounds are also any
compounds used in prior art in Ziegler-Natta catalyst synthesis.
Suitable compounds are compounds of magnesium, e.g., Grignard
reagents, magnesium dialkyls, and magnesium halides.
The thus-formed catalyst precursor is optionally contacted with at
least one pre-reducing agent, e.g., tri-n-hexyl aluminum, or
diethyl aluminum chloride, prior to activation with TMA. The amount
of the pre-reducing agent may be adjusted as described by Karol et
al, European Patent Application No. 84103441.6, to obtain a
favorable balance of catalyst productivity and settled bulk density
of the resin. The pre-reduced precursor is then activated either
outside of the reactor vessel or inside the vessel with the
trimethylaluminum catalyst activator.
The TMA activator is employed in an amount which is at least
effective to promote the polymerization activity of the solid
component of the catalyst of this invention. Preferably, the TMA
activator is used in such amounts that the concentration thereof in
the polymer product is about 15 to about 300 parts per million
(ppm), preferably it is about 30 to about 150 ppm, and most
preferably about 40 to about 80 ppm. In slurry polymerization
processes, a portion of the TMA activator can be employed to
pretreat the polymerization medium if desired.
The catalyst may be activated in situ by adding the activator and
catalyst separately to the polymerization medium. It is also
possible to combine the catalyst and activator before the
introduction thereof into the polymerization medium, e.g., for up
to about 2 hours prior to the introduction thereof into the
polymerization medium at a temperature of from about -40.degree. to
about 100.degree. C.
A suitable activating amount of the activator may be used to
promote the polymerization activity of the catalyst. The
aforementioned proportions of the activator can also be expressed
in terms of the number of moles of activator per gram atom of
titanium in the catalyst composition, e.g., from about 6 to about
80, preferably about 8 to about 30 moles of activator per gram atom
of titanium.
Alpha-olefins may be polymerized with the catalysts prepared
according to the present invention by any suitable process. Such
processes include polymerizations carried out in suspension in
solution or in the gas phase. Gas phase polymerization reactions
are preferred, e.g., those taking place in stirred bed reactors
and, especially, fluidized bed reactors.
The molecular weight of the polymer may be controlled in a known
manner, e.g., by using hydrogen. With the catalysts produced
according to the present invention, molecular weight may be
suitably controlled with hydrogen when the polymerization is
carried out at relatively low temperatures, e.g., from about
70.degree. to about 105.degree. C. The molecular weight control is
evidenced by a measurable positive change in melt index (I.sub.2)
of the polymer when the molar ratio of hydrogen to ethylene in the
reactor is increased.
We found that the average molecular weight of the polymer is also
dependent on the amount of the TMA activator employed. Increasing
the TMA concentration in the reactor gives small, positive changes
in melt index.
The molecular weight distribution of the polymers prepared in the
presence of the catalysts of the present invention, as expressed by
the melt flow ratio (MFR) values, varies from about 24 to about 29
for LLDPE products having a density of about 0.914 to about 0.926
gms/cc, and an I.sub.2 melt index of about 0.9 to about 4.0. As is
known to those skilled in the art, such MFR values are indicative
of a relatively narrow molecular weight distribution, thereby
rendering the polymers especially suitable for low density film
applications since the products exhibit less molecular orientation
in high-speed film blowing processes, and therefore have greater
film strength.
The polymers produced with the catalyst compositions of the present
invention have about 20-30% lower hexane extractables than the
polymers prepared with catalysts activated with triethylaluminum
(TEAL) or triisobutylaluminum (TIBA), both of which were commonly
used as catalyst activators in prior art. The physical properties
of the films made from the resins polymerized with the catalysts of
this invention are also better than those made from the resins
polymerized with the TEAL- and TIBA-activated catalysts. For
example, the films of the present invention exhibit about 20-30%
improvement in dart drop and machine dimension (MD) tear properties
than the films prepared with such previously-known catalysts. The
films also exhibit about 30% to about 40% lower relaxation time and
about 20% lower die swell characteristics than films prepared with
the heretofore known catalyst compositions.
Dart drop is defined herein by A.S.T.M. D-1709, Method A; with a
3.81 mm dart, and a drop height of 0.66 meters.
Melt relaxation time is defined herein as the time for shear stress
in a polymer melt at 190.degree. C. to decay to 10% of its steady
value after cessation of steady shear flow of 0.1 sec.sup.-1.
Die swell is defined herein as the diameter of the extrudate
divided by the diameter of the die using an extrusion plastometer,
as described by A.S.T.M. D-1238.
The higher alpha-olefin incorporation properties of the catalysts
of this invention are also improved as compared to TEAL- and
TIBA-activated catalysts as evidenced by the lower mole ratio of
higher alpha-olefin/ethylene necessary to produce resins of a
certain melt index and density.
The catalysts prepared according to the present invention are
highly active, their productivity is at least about 1,000, and can
be as much as about 10,000, grams of polymer per gram of catalyst
precursor per 100 psi of ethylene partial pressure.
The polyethylene polymers prepared in accordance with the present
invention may be homopolymers of ethylene or copolymers of ethylene
with one or more C.sub.3 -C.sub.10 alpha-olefins. Thus, copolymers
having two monomeric units are possible as well as terpolymers
having three monomeric units. Particular examples of such polymers
include ethylene/1-butene copolymers, ethylene/1-hexene copolymers,
ethylene/4-methyl-1-pentene copolymers, ethylene/1-butene/1-hexene
terpolymers, ethylene/propylene/1-hexene terpolymers and
ethylene/propylene/1-butene terpolymers. When propylene is employed
as a comonomer, the resulting linear low density polyethylene
polymer preferably has at least one other alpha-olefin comonomer
having at least four carbon atoms in an amount of at least 1
percent by weight of the polymer. Accordingly, ethylene/propylene
copolymers are possible, but not preferred. The most preferred
polymers are copolymers of ethylene and 1 -hexene, and copolymers
of ethylene and 1-butene.
The linear low density polyethylene polymers produced in accordance
with the present invention preferably contain at least about 80
percent by weight of ethylene units. .Iadd.Such linear low density
polyethylene polymers have a density of about 0.940 g/cc or less
and they are copolymers of ethylene and at least one C.sub.3
-C.sub.10 alpha-olefin. .Iaddend.
A particularly desirable method for producing linear low density
polyethylene polymers according to the present invention is in a
fluid bed reactor. Such a reactor and means for operating the same
is described by Levine et al, U.S. Pat. No. 4,011,382 and Karol et
al, U.S. Pat. No. 4,302,566, the entire contents of both of which
being incorporated herein by reference, and by Nowlin et al, U.S.
Pat. No. 4,481,301.
The following Examples further illustrate the essential features of
the invention. However, it will be apparent to those skilled in the
art that the specific reactants and reaction conditions used in the
Examples do not limit the scope of the invention.
The properties of the polymers produced in the Examples were
determined by the following test methods:
Density: ASTM D-1505--A plaque is made and conditioned for one hour
at 100.degree. C. to approach equilibrium crystallinity.
Measurement for density is then made in a density gradient column;
reported as gms/cc.
Melt Index (MI), I.sub.2 : ASTM D-1238--Condition E--Measured at
190.degree. C.--reported as grams per 10 minutes.
High Load Melt Index (HLMI), I.sub.2 : ASTM D-1238--Condition
F--Measured at 10.5 times the weight used in the melt index test
above.
Melt Flow Ratio (MFR)=I.sub.21 /I.sub.2
Productivity: A sample of the resin product is ashed, and the
weight % of ash is determined; since the ash is essentially
composed of the catalyst, the productivity is thus the pounds of
polymer produced per pound of total catalyst consumed. The amount
of Ti, Mg and Cl in the ash are determined by elemental
analysis.
Settled Bulk Density: The resin is poured via 1" diameter funnel
into a 100 mil graduated cylinder to 100 mil line without shaking
the cylinder, and weighed by difference. The cylinder is then
vibrated for 5-10 minutes until the resin level drops to a final,
steady-state level. The settled bulk density is taken as the
indicated cylinder volume at the settled level, divided by the
measured resin weight.
n-hexane extractables: (FDA test used for polyethylene film
intended for food contact applications). A 200 square inch sample
of 1.5 mil gauge film is cut into strips measuring 1".times.6" and
weighed to the nearest 0.1 mg. The strips are placed in a vessel
and extracted with 300 ml of n-hexene at 50.degree..+-.1.degree. C.
for 2 hours. The extract is then decanted into tared culture
dishes. After drying the extract in a vacuum dessicator the culture
dish is weighed to the nearest 0.1 mg. The extractables, normalized
with respect to the original sample weight, is then reported as the
weight fraction of n-hexane extractables.
Machine Direction Tear, MD.sub.TEAR (gm/mil): ASTM D-1922
EXAMPLE 1
Catalyst precursor Synthesis
All procedures were carried out in clean, commercial scale
equipment under purified nitrogen, or dry air. All solvents were
pre-dried and nitrogen-purged. This catalyst precursor was prepared
substantially according to the disclosure of Hagerty et al, U.S.
Pat. No. 4,562,169.
Precursor Preparation
First Step:
348 kgs of Davison 955 silica was heated at 825.degree. C. for
about 4 hours in an atmosphere of dry air (Analysis: OH=0.53
mmoles/gm). The silica was then transferred into a 4000 liter mix
vessel under a slow nitrogen purge. The mix vessel was equipped
with a ribbon-type mechanical stirrer to provide mixing of the
internal contents. Approximately 27000 liters of dry isopentane was
added while stirring, and the resulting slurry was heated to
70.degree. C. 160 kgs of a 2.28 molar solution of ethylmagnesium
chloride (EtMgCl) in tetrahydrofuran (THF) was added through a
spray nozzle over a 60 minute period while stirring. The slurry was
mixed for an additional 60 minutes to complete reaction. Then the
solvent was removed by distillation at 70.degree. C., and the
product was dried at 82.degree. C. for about 55 hours with a slow
nitrogen purge to yield a free-flowing powder. Analysis: Mg=2.54
wt. %, THF=4.55 wt. %.
Second Step:
The product from the first step was held in the mix vessel under a
dry nitrogen atmosphere at 62.degree. C., while stirring. 1700
liters of dry isopentane was fed to the mix vessel simultaneously
with 300 kgs of TiCl.sub.4 through a common feed line. The addition
time was approximately 90 minutes. The mix vessel's internal
temperature was then raised to 80.degree. C. and held for 2 hours
to complete reaction. The solids were allowed to settle, and the
supernatant liquid was withdrawn through a dip-tube. The product
was washed nine (9) times with 2000 l portions of isopentane to
remove excess TiCl.sub.4. The product was then dried for 8.5 hours
with a slow nitrogen purge at 60.degree. C. The resulting catalyst
precursor product was analyzed as follows: Mg=2.23 wt. %; Ti=3.33
wt. %; Cl=1.20 wt. % THF=1.91 wt. %.
EXAMPLE 2
Preparation of LLDPE Product With TEAL -Activated Precursor of
Example 1
The catalyst precursor composition of example 1 was used to prepare
a linear low density polyethylene product (LLDPE) in a fluid bed,
pilot plant reactor operated substantially in the manner disclosed
by Nowlin et al, U.S. Pat. No. 4,481,301. The reactor was 0.45
meters in diameter and it was capable of producing up to 25 kgs/hr
of resin. A steady-state reaction was obtained by continuously
feeding catalyst precursors, TEAL activator, and reactant gases
(ethylene, 1-hexane and hydrogen) to the reactor while also
continuously withdrawing polymer product from the reactor. The feed
rate of ethylene was maintained at a constant 13.0 kgs/hr, and the
feed rate of catalyst precursor was adjusted to achieve a
substantially equal rate of polymer production. The feed rate of
TEAL was 4.69 gms/hr, equivalent to a 361 ppm feed ratio of TEAL to
ethylene. Reaction temperature was 88.degree. C., superficial gas
velocity was 0.45 meters/sec, and fluid bed residence time was
approximately 5 hours. Other reaction conditions, including gas
phase composition in the reactor, are given in Table 1.
Catalyst productivity was determined by dividing the polymer
production rate by the catalyst feed rate. A value of 5270 grams of
polymer per gram of catalyst precursor was thereby obtained (Table
I). The polymer product was evaluated in a conventional manner, and
the results are summarized in Table II.
EXAMPLE 3
Preparation of LLDPE Products with TMA-Activated Precursor of
Example 1
LLDPE polymer was produced with the catalyst precursor of Example
1, using substantially the same reaction conditions as in Example
2, except that TMA was used as the activator in place of TEAL. The
TMA feed ratio to ethylene was 156 ppm. Reaction conditions are
summarized in Table I, and product properties are summarized in
Table II.
TABLE I
__________________________________________________________________________
(Precursor of Example 1) Activator Catalyst Productivity Ex.
Activator Feed Ratio .sup.P C.sub.2 .dbd. Mole Ratio (gms
polymer/gms No. Type (ppm) (psi) 1-C.sub.6 .dbd./C.sub.2 .dbd.
H.sub.2 /C.sub.2 .dbd. catalyst precursor)
__________________________________________________________________________
2 TEAL 182 93 0.141 0.239 5270 3 TMA 187 95 0.115 0.229 4450
__________________________________________________________________________
TABLE II
__________________________________________________________________________
Resin Properties (Precursor of Example 1) Settled Bulk Ex. Density
I.sub.21 FDA Extract Density MD Tear No. (gm/cc) (gms/10 min) MFR
(wt. %) (lbs/ft.sup.3) (gms/mil)
__________________________________________________________________________
2 0.9169 54.5 32.3 6.51 21.3 332 3 0.9152 48.8 32.5 7.37 24.3 324
__________________________________________________________________________
Comparison of TEAL Versus TMA In Examples 2 and 3
The use of TMA activator in place of TEAL produced at catalyst
composition with somewhat less productivity (grams of polymer per
gram of catalyst precursor). The catalyst productivity in Example 3
was reduced by 16% in comparison with Example 2 (Table I) at an
approximately constant level of ethylene partial pressure (.sup.P
C.sub.2 .dbd.).
The comonomer incorporation was significantly improved with TMA, as
indicated by an 18% lower gas phase molar ratio of 1-hexene to
ethylene (1-C.sub.6 .dbd./C.sub.2 .dbd.) that was required to
produce a product density in the 0.915 to 0.917 gms/cc density
range (Tables I and II).
FDA extractables were higher with TMA (7.37 wt. %) than with TEAL
(6.15%). This difference is believed to be the result of the lower
polymer density obtained in Example 3 (0.9152 gms/cc) in comparison
with Example 2 (0.9169 gms/cc). Lower density LLDPE polymers
inherently exhibity higher levels of extractable material. The
apparent difference in FDA extractables between the polymers of
Examples 2 and 3 is therefore not believed to be a fundamental
difference between TMA and TEAL activators.
Polymer settled bulk density was approximately 14% higher with the
TMA activator-containing catalyst in comparison with the TEAL
activator-containing catalyst (Table II).
EXAMPLE 4
Catalyst Precursor Synthesis
Another catalyst precursor was synthesized according to the
teachings of Karol et al, European Patent Application No.
84103441.6, filed on Mar. 28, 1984, Publication No. 0 120 503,
published on Oct. 3, 1984. This catalyst precursor is substantially
equivalent to that of Karol et al, as disclosed in the
aforementioned Published European Patent Application. It is also
substantially equivalent to the precursors prepared by the
following representative procedure.
(a) Impregnation of Support with Precursor
In a 12 liter flask equipped with a mechanical stirrer were placed
41.8 g (0.439 mol) of anhydrous MgCl.sub.2 and 2.5 liters of
tetrahydrofuran (THF). To this mixture, 29.0 (0.146 mol) of
TiCl.sub.3 .multidot.0.33AlCl.sub.3 were added dropwise over a 1/2
hour period. The mixture was then heated at 60.degree. C. for
another 1/2 hour in order to completely dissolve the material.
Five hundred grams (500 g) of silica were dehydrated by heating at
a temperature of 600.degree. C. and slurried in 3 liters of
isopentane. The slurry was stirred while 186 ml of a 20 percent by
weight solution of triethylaluminum in hexane was added thereto
over a 1/4 hour period. The resulting mixture was then dried under
a nitrogen purge at 60.degree. C. over a period of about 4 hours to
provide a dry, free-flowing powder containing 5.5 percent by weight
of the aluminum alkyl.
The treated silica was then added to the solution prepared as
above. The resulting slurry was stirred for 1/4 hour and then dried
under a nitrogen purge at 60.degree. C. over a period of about 4
hours to provide a dry, impregnated, free-flowing powder.
(b) Preparation of Partially Activated Precursor
(i) The silica-impregnated precursor composition prepared in
accordance with Example 4(a) was slurried in 3 liters of anhydrous
isopentane and stirred while a 20 percent by weight solution of
diethylaluminum chloride in anhydrous hexane was added thereto over
a 1/4 hour period. The diethylaluminum chloride (DEAC) solution was
employed in an amount sufficient to provide 0.4 mols of this
compound per mol of tetrahydrofuran (THF) in the precursor. After
addition of the diethylaluminum chloride was completed, stirring
was continued for an additional 1/4 to 1/2 hour while a 20 percent
by weight solution of tri-n-hexylaluminum (TNHAL) in anhydrous
hexane was added in an amount sufficient to provide 0.6 mols of
this compound per mol of tetrahydrofuran in the precursor. The
mixture was then dried under a nitrogen purge at a temperature of
65.degree..+-.10.degree. C. over a period of about 4 hours to
provide a dry, free-flowing powder. This material was stored under
dry nitrogen until it was needed.
Two alternative procedures (ii) and (iii) for partially activating
the precursor may be employed. (ii) The silica-impregnated
precursor composition prepared in accordance with Example 4(a) was
partially activated with diethylaluminum chloride and
tri-n-hexylaluminum employing the same procedure as in 4(b)(i)
except that the tri-n-hexylaluminum was employed in an amount
sufficient to provide 0.4 mols of this compound per mol of
tetrahydrofuran in the precursor.
(iii) The silica-impregnated precursor composition prepared in
accordance with Example 4(a) was partially activated with
diethylaluminum chloride and tri-n-hexylaluminum employing the same
procedure as in 2(a) except that each compound was employed in an
amount sufficient to provide 0.3 mols of such compound per mol of
tetrahydrofuran in the precursor.
EXAMPLE 5
Preparation of LLDPE Product With TEAL-Activated Precursor of
Example 4
The partially activated catalyst precursor composition of Example
4, with the molar ratios of DEAC/THF=0.36 and TNHAL/THF=0.25, was
used to prepare LLDPE product in a fluid bed, pilot plant reactor.
Reaction conditions were substantially equivalent to those of
Examples 2 and 3, except that the reaction temperature was
86.degree. C. Other reaction conditions are summarized in Table
III. The product properties were determined in a conventional
manner and are summarized in Table IV.
EXAMPLE 6-10
Preparation of LLDPE Products with TMA-Activated Precursor of
Example 4
The partially activated precursor composition of Example 4, with
the molar ratios of DEAC/THF=0.36 and TNHAL/THF=0.25, was used to
prepare LLDPE product in a fluid bed, pilot plant reactor. Reaction
conditions were substantially equivalent to those of Example 5,
except that a TMA activator was used in place of TEAL, and
adjustments were made to the activator feed ratio and ethylene
partial pressure (.sup.P C.sub.2 .dbd.) to determine the separate
effects of these variables. Reaction conditions are summarized in
Table III, and the product properties are summarized in Table
IV.
The hydrogen to ethylene molar ratio in the reactor (H.sub.2
/C.sub.2 .dbd.) was adjusted as required to obtain a high load melt
index (I.sub.21) of about 30 gms/10 min. Different levels of
H.sub.2 /C.sub.2 .dbd. were required depending on the TMA activator
feed ratio (Table III).
TABLE III
__________________________________________________________________________
Reaction Conditions (Precursor of Example 4) Activator/ Ex.
Activator C.sub.2 .dbd. Feed .sup.P C.sub.2 .dbd. 1-C.sub.6
.dbd./C.sub.2 .dbd. H.sub.2 /C.sub.2 .dbd. Productivity No. Type
(ppm) (psi) (moles/moles) (moles/moles) (gms/gm)
__________________________________________________________________________
5 TEAL 361 89 0.149 0.129 4190 6 TMA 156 93 0.139 0.177 3320 7 TMA
71 86 0.148 0.170 4000 8 TMA 74 90 0.149 0.215 3640 9 TMA 240 94
0.142 0.162 2580 10 TMA 245 129 0.143 0.161 4510
__________________________________________________________________________
TABLE IV
__________________________________________________________________________
Resin Properties (Precursor of Example 4) Settled Bulk Ex. Density
I.sub.21 FDA Extract Density MD Tear No. (gm/cc) (gms/10 min) MFR
(wt. %) (lbs/ft.sup.3) (gms/mil)
__________________________________________________________________________
5 0.9160 31.0 32.3 6.05 25.5 266 6 0.9166 31.6 28.5 4.54 25.2 310 7
0.9159 22.4 28.7 3.69 25.4 345 8 0.9165 34.9 28.6 3.86 25.9 382 9
0.9159 26.6 27.1 4.02 25.9 321 10 0.9169 32.2 28.3 4.37 25.4 356
__________________________________________________________________________
Discussion Of Examples 6-10
The various levels of ethylene partial pressure and TMA activator
feed ratios used in Examples 6-10 had no substantial effect on
product properties. As indicated in Table IV, the polymer MFR, FDA
extractables, settled bulk density, and MD tear strength were
essentially the same in Examples 6 through 10.
However, the productivity of the TMA-activated precursor was found
to be strongly dependent on the ethylene partial pressure and
activator feed ratio. The ethylene partial pressure effect is
illustrated by comparing Examples 9 and 10 Table III: the
productivity at 129 psi ethylene partial pressure was approximately
75% higher than at 94 psi. This effect is typical for Ziegler
catalysts, including those disclosed by Nowlin et al, U.S. Pat. No.
4,481,301.
The effect on productivity of various activator feed ratios is
illustrated in FIG. 1, which is a graphical representation of the
data of Examples 6-9. The highest level of productivity are
attained with relatively low activator feed ratios. A similar
effect is known to exist with certain Ziegler catalyst compositions
activated with TEAL, such as those of Example 1, although it is not
present with the catalyst composition disclosed by Karol et al in
the aforementioned European Patent Application (i.e., activated
with TEAL). In the case of the Karol et al catalyst, the
productivity is not sensitive to the TEAL feed ratio over a broad
range.
Comparison Of TEAL Versus TMA In Examples 5-10
The catalyst composition of the present invention produced polymer
with lower melt flow ratio (MFR), lower FDA extractables, and
higher MD tear strength in comparison with the prior art
composition of Karol et al. However, unlike the previous Examples 2
and 3, there were no differences noted in settled bulk density or
in comonomer incorporation (e.g., 1-C.sub.6 .dbd./C.sub.2 .dbd.
ratio in the reactor required to attain a density of 0.917
gms/cc).
The melt flow ratio in Table IV was reduced from 32.3 (Example 5
with TEAL) to an average of 28.2 (Examples 6-10 with TMA). FDA
extractables were reduced by an average of 32%, and MD tear
strength was increased by an average of 29%, in the same
examples.
It will be apparent to those skilled in the art that the specific
embodiments discussed above can be successfully repeated with
ingredients equivalent to those generically or specifically set
forth above and under variable process conditions.
From the foregoing specification, one skilled in the art can
readily ascertain the essential features of this invention and
without departing from the spirit and scope thereof can adapt it to
various diverse applications.
* * * * *