U.S. patent application number 16/126243 was filed with the patent office on 2019-01-03 for process for preparing a polyethylene in at least one continuously stirred tank reactor.
The applicant listed for this patent is Total Research & Technology Feluy. Invention is credited to Martine Slawinski, Aurelien Vantomme, Alexandre Welle, Christopher Willocq.
Application Number | 20190002603 16/126243 |
Document ID | / |
Family ID | 50897492 |
Filed Date | 2019-01-03 |
United States Patent
Application |
20190002603 |
Kind Code |
A1 |
Vantomme; Aurelien ; et
al. |
January 3, 2019 |
Process for Preparing a Polyethylene in at Least One Continuously
Stirred Tank Reactor
Abstract
Processes for preparing a polyethylene in at least one
continuously stirred tank reactor are described herein. The process
may comprise the step of: polymerizing ethylene in the presence of
at least one supported metallocene catalyst, a diluent, optionally
one or more co-monomers, and optionally hydrogen, thereby obtaining
the polyethylene, wherein the supported metallocene catalyst
comprises a solid support, a co-catalyst and at least one
metallocene, wherein the solid support has a surface area within
the range of from 100 to 500 m2/g, and has a D50 value within the
range of from 4 .mu.m to 18 .mu.m, with D50 being defined as the
particle size for which fifty percent by weight of the particles
has a size lower than the D50; and D50 being measured by laser
diffraction analysis on a Malvern type analyzer. Polyethylene
obtained by the disclosed process and articles comprising the
polyethylene are also described.
Inventors: |
Vantomme; Aurelien;
(Mignault, BE) ; Willocq; Christopher; (Bousval,
BE) ; Welle; Alexandre; (Court-St. Etienne, BE)
; Slawinski; Martine; (Nivelles, BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Total Research & Technology Feluy |
Seneffe (Feluy) |
|
BE |
|
|
Family ID: |
50897492 |
Appl. No.: |
16/126243 |
Filed: |
September 10, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15318010 |
Dec 12, 2016 |
10100135 |
|
|
PCT/EP2015/063006 |
Jun 11, 2015 |
|
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16126243 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08F 10/02 20130101;
C08F 4/025 20130101; C08F 110/02 20130101; C08F 2420/04 20130101;
C08F 4/02 20130101; C08F 2500/05 20130101; C08F 2500/18 20130101;
C08F 4/6592 20130101; C08F 4/65916 20130101; C08F 110/02 20130101;
C08F 4/65927 20130101; C08F 110/02 20130101; C08F 4/65916 20130101;
C08F 110/02 20130101; C08F 2/14 20130101; C08F 110/02 20130101;
C08F 2500/18 20130101; C08F 2500/24 20130101; C08F 2500/07
20130101 |
International
Class: |
C08F 10/02 20060101
C08F010/02; C08F 4/02 20060101 C08F004/02; C08F 110/02 20060101
C08F110/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 12, 2014 |
EP |
14172170.4 |
Claims
1.-15. (canceled)
16. An article comprising a polyethylene resin prepared by a
process in at least one continuously stirred tank reactor, the
process comprising: polymerizing ethylene in the presence of at
least one supported metallocene catalyst, a diluent, optionally one
or more co-monomers, and optionally hydrogen, thereby obtaining the
polyethylene resin, wherein the supported metallocene catalyst
comprises a solid support, a co-catalyst and at least one
metallocene, wherein the solid support has a surface area within
the range of from 100 to 350 m.sup.2/g, and has a D50 value within
the range of from 4 .mu.m to 18 .mu.m, with D50 being defined as
the particle size for which fifty percent by weight of the
particles has a size lower than the D50; and D50 being measured by
laser diffraction analysis on a Malvern type analyzer.
17. The article according to claim 16, wherein the polyethylene
resin at the end of the process has a D50 of at least 100 and at
most 400 .mu.m; and Si content lower than 60 ppm by weight.
18. The article according to claim 16, wherein the at least one
supported metallocene catalyst comprises a silica-containing
support, an alumoxane, and least one metallocene.
19. The article according to claim 16, wherein the at least one
supported metallocene catalyst comprises a silica- and
titania-containing support an alumoxane, and least one
metallocene.
20. The article according to claim 19, wherein the supported
catalyst has a Ti content of from 0.1 to 10% by weight based on the
total weight of the supported metallocene catalyst, preferably from
0.5 to 5% by weight, and most preferably from 1.0 to 2.5% by
weight.
21. The article according to claim 20, wherein the solid support of
the at least one supported metallocene catalyst has an average pore
volume of at least 1.0 and at most 3.0 ml/g, preferably at least
1.0 and at most 2.5 ml/g, more preferably at least 1.2 and at most
2.0 ml/g.
22. The article according to claim 16, wherein the metallocene
catalyst is a compound of formula (I) or (II) (Ar)2MQ2 (I)
R''(Ar)2MQ2 (II) wherein the metallocenes according to formula (I)
are non-bridged metallocenes and the metallocenes according to
formula (II) are bridged metallocenes; wherein the metallocene
according to formula (I) or (II) has two Ar bound to M which can be
the same or different from each other; wherein Ar is an aromatic
ring, group or moiety and wherein each Ar is independently selected
from the group consisting of cyclopentadienyl, indenyl (IND),
tetrahydroindenyl (THI), and fluorenyl, wherein each of the groups
may be optionally substituted with one or more substituents each
independently selected from the group consisting of halogen, and a
hydrocarbyl having 1 to 20 carbon atoms, and wherein the
hydrocarbyl optionally contains one or more atoms selected from the
group comprising B, Si, S, O, F, and P; wherein M is a transition
metal selected from the group consisting of titanium, zirconium,
hafnium, and vanadium; and preferably is zirconium; wherein each Q
is independently selected from the group consisting of halogen, a
hydrocarboxy having 1 to 20 carbon atoms, and a hydrocarbyl having
1 to 20 carbon atoms and wherein the hydrocarbyl optionally
contains one or more atoms selected from the group comprising B,
Si, S, O, F, and P; and wherein R'' is a divalent group or moiety
bridging the two Ar groups and selected from the group consisting
of C1-C20 alkylene, germanium, silicon, siloxane, alkylphosphine,
and an amine, and wherein the R'' is optionally substituted with
one or more substituents each independently selected from the group
consisting of halogen, a hydrocarbyl having 1 to 20 carbon atoms,
and wherein the hydrocarbyl optionally contains one or more atoms
selected from the group comprising B, Si, S, O, F, and P.
23. The article according to claim 16, wherein the metallocene is a
compound selected from one of the following formula (III) or (IV):
##STR00003## wherein each R in formula (III) or (IV) is the same or
different and is selected independently from hydrogen or XR'v in
which X is chosen from Group 14 of the Periodic Table, oxygen or
nitrogen and each R' is the same or different and is chosen from
hydrogen or a hydrocarbyl of from 1 to 20 carbon atoms and v+1 is
the valence of X, R'' is a structural bridge between the two
indenyl or tetrahydrogenated indenyls that comprises a C1 C4
alkylene radical, a dialkyl germanium, silicon or siloxane, or an
alkyl phosphine or amine radical; Q is a halogen or a hydrocarbyl
radical having from 1 to 20 carbon atoms, preferably Q is F, Cl or
Br; and M is a transition metal selected from the group consisting
of titanium, zirconium, hafnium, and vanadium; and preferably is
zirconium.
24. The article according to claim 16, wherein the metallocene
catalyst comprises a bridged unsubstituted bis-indenyl and/or a
bridged unsubstituted bis-tetrahydrogenated indenyl.
25. The article according to claim 16, wherein the solid support of
the at least one supported metallocene catalyst has a particle size
distribution of a span value lower than 2.0, preferably has a span
value of at least 0.9 and at most 1.3, wherein the span is defined
as: span = D 90 - D 10 D 50 ##EQU00002## with D90 being defined as
the particle size for which ninety percent by weight of the
particles has a size lower than the D90; with D10 being defined as
the particle size for which ten percent by weight of the particles
has a size lower than the D10; with D50 being defined as the
particle size for which fifty percent by weight of the particles
has a size lower than the D50; and with the D90, D10 and D50 being
measured by laser diffraction analysis on a Malvern type
analyzer.
26. The article according to claim 16, wherein the co-monomer is
1-butene.
27. The article according to claim 16, wherein the polymerization
process is performed in the presence of at least one antifouling
agent.
28. The article according to claim 16, wherein the process is
performed in at least two continuously stirred tank reactors
connected in series.
29. The article according to claim 16, wherein the diluent is
selected from hexane, isohexane, or heptane
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The invention is in the field of polymers technology. In
particular, the present invention relates to a process for
preparing a polyethylene.
BACKGROUND OF THE INVENTION
[0002] Polyethylene (PE) is synthesized by polymerizing ethylene
(CH.sub.2.dbd.CH.sub.2) monomers. Because it is cheap, safe, stable
to most environments and easy to be processed, polyethylene
polymers are useful in many applications. According to the
properties, polyethylene can be classified into several types, such
as but not limited to LDPE (Low Density Polyethylene), LLDPE
(Linear Low Density Polyethylene), and HDPE (High Density
Polyethylene). In another classification, the used polyethylene can
be classified as Ultra High Molecular Weight (UHMW), High Molecular
Weight (HMW), Medium Molecular Weight (MMW) and Low Molecular
Weight (LMW). Each type of polyethylene has different properties
and characteristics.
[0003] Ethylene polymerization processes are frequently carried out
in a loop reactor using ethylene monomer, liquid diluent and
catalyst, optionally one or more co-monomer(s), optionally an
activating agent or co-catalyst and optionally hydrogen. The
polymerization in a loop reactor is usually performed under slurry
conditions, with the produced polymer usually in the form of solid
particles which are suspended in the diluent. The slurry in the
reactor is circulated continuously with a pump to maintain
efficient suspension of the polymer solid particles in the liquid
diluent. Polymer slurry is discharged from the loop reactor. After
the polymer product is collected from the reactor and the
hydrocarbon residues are removed, the polymer product is dried,
additives can be added and finally the polymer may be mixed and
pelletized. The resulting product can then be used for the
manufacturing of various objects.
[0004] Polymerization of polyolefin such as polyethylene can also
be performed in continuous stirred tank reactors (CSTR). These
polymerizations in CSTR are usually performed in the presence of
Ziegler-Natta catalysts. Metallocene catalysts are not preferred
because of lower intrinsic activity combined with shorter life time
and higher sensitivity to contaminants. Intrinsically Ziegler-Natta
catalysts lead to poorer product properties due to multiple site
behavior. Additionally, Ziegler-Natta catalysts have limited
comonomer response and lead to significant amount of polymer chains
dissolved in the continuous phase.
[0005] Therefore, it is an object of the present invention to
provide a process for preparing polyethylene prepared in at least
one continuous stirred tank reactor having improved properties.
SUMMARY OF THE INVENTION
[0006] It is the finding of the present invention that the above
object can be achieved by a process as presently claimed.
[0007] According to a first aspect, the present invention relates
to a process for preparing a polyethylene in at least one
continuously stirred tank reactor, comprising the step of:
polymerizing ethylene in the presence of at least one supported
metallocene catalyst, a diluent, optionally one or more
co-monomers, and optionally hydrogen, thereby obtaining the
polyethylene, wherein said supported metallocene catalyst comprises
a solid support, a co-catalyst and at least one metallocene,
wherein the solid support has a surface area within the range of
from 100 to 500 m.sup.2/g, and has a D50 value within the range of
from 4 .mu.m to 18 .mu.m, with D50 being defined as the particle
size for which fifty percent by weight of the particles has a size
lower than the D50; and D50 being measured by laser diffraction
analysis on a Malvern type analyzer.
[0008] The present invention further encompasses a polyethylene
obtained by the process according to the first aspect of the
invention.
[0009] The present invention also encompasses an article comprising
a polyethylene prepared by the process according to the first
aspect of the invention.
[0010] The present inventors have found that the present process
allowed the preparation of small particle size polymer resin
resulting in improved polymer properties, such as homogeneity of
bimodal resin, and that the articles prepared with said
metallocene-catalyzed polyethylene resin exhibited better
mechanical and optical properties than articles prepared with
Ziegler Natta catalyzed polyethylene resins.
[0011] The independent and dependent claims set out particular and
preferred features of the invention. Features from the dependent
claims may be combined with features of the independent or other
dependent claims as appropriate. The present invention will now be
further described. In the following passages, different aspects of
the invention are defined in more detail. Each aspect so defined
may be combined with any other aspect or aspects unless clearly
indicated to the contrary. In particular, any feature indicated as
being preferred or advantageous may be combined with any other
feature or features indicated as being preferred or
advantageous.
DETAILED DESCRIPTION OF THE INVENTION
[0012] Before the present method used in the invention is
described, it is to be understood that this invention is not
limited to particular process, polyethylene resins, or articles
described, as such process, polyethylene resins, or articles may,
of course, vary. It is also to be understood that the terminology
used herein is not intended to be limiting, since the scope of the
present invention will be limited only by the appended claims.
[0013] When describing the processes of the invention, the terms
used are to be construed in accordance with the following
definitions, unless a context dictates otherwise.
[0014] As used herein, the singular forms "a", "an", and "the"
include both singular and plural referents unless the context
clearly dictates otherwise. By way of example, "a resin" means at
least one resin.
[0015] The terms "comprising", "comprises" and "comprised of" as
used herein are synonymous with "including", "includes" or
"containing", "contains", and are inclusive or open-ended and do
not exclude additional, non-recited members, elements or method
steps. The terms "comprising", "comprises" and "comprised of" also
include the term "consisting of".
[0016] The recitation of numerical ranges by endpoints includes all
integer numbers and, where appropriate, fractions subsumed within
that range (e.g. 1 to 5 can include 1, 2, 3, 4 when referring to,
for example, a number of elements, and can also include 1.5, 2,
2.75 and 3.80, when referring to, for example, measurements). The
recitation of end points also includes the end point values
themselves (e.g. from 1.0 to 5.0 includes both 1.0 and 5.0). Any
numerical range recited herein is intended to include all
sub-ranges subsumed therein.
[0017] Reference throughout this specification to "one embodiment"
or "an embodiment" means that a particular feature, structure or
characteristic described in connection with the embodiment is
included in at least one embodiment of the present invention. Thus,
appearances of the phrases "in one embodiment" or "in an
embodiment" in various places throughout this specification are not
necessarily all referring to the same embodiment, but may.
Furthermore, the particular features, structures or characteristics
may be combined in any suitable manner, as would be apparent to a
person skilled in the art from this disclosure, in one or more
embodiments. Furthermore, while some embodiments described herein
include some but not other features included in other embodiments,
combinations of features of different embodiments are meant to be
within the scope of the invention, and form different embodiments,
as would be understood by those in the art. For example, in the
following claims, any of the claimed embodiments can be used in any
combination.
[0018] Unless otherwise defined, all terms used in disclosing the
invention, including technical and scientific terms, have the
meaning as commonly understood by one of ordinary skill in the art
to which this invention belongs. By means of further guidance,
definitions for the terms used in the description are included to
better appreciate the teaching of the present invention.
[0019] Preferred statements (features) and embodiments of this
invention are set herein below. Each statement and embodiment of
the invention so defined may be combined with any other statement
and/or embodiment unless clearly indicated to the contrary. In
particular, any feature indicated as being preferred or
advantageous may be combined with any other feature or features or
statements indicated as being preferred or advantageous. Hereto,
the present invention is in particular captured by any one or any
combination of one or more of the below numbered aspects and
embodiments 1 to 47, with any other statement and/or embodiment.
[0020] 1. A process for preparing a polyethylene in at least one
continuously stirred tank reactor, comprising the step of:
polymerizing ethylene in the presence of at least one supported
metallocene catalyst, a diluent, optionally one or more
co-monomers, and optionally hydrogen, thereby obtaining the
polyethylene, [0021] wherein said supported metallocene catalyst
comprises a solid support, a co-catalyst and at least one
metallocene, [0022] wherein the solid support has a surface area
within the range of from 100 to 500 m.sup.2/g, preferably from 150
m.sup.2/g to 400 m.sup.2/g, preferably from 200 m.sup.2/g to 350
m.sup.2/g, preferably from 200 m.sup.2/g to 300 m.sup.2/g, and
preferably from 250 m.sup.2/g to 300 m.sup.2/g; and has a D50 value
within the range of from 3 .mu.m to 25 .mu.m, with D50 being
defined as the particle size for which fifty percent by weight of
the particles has a size lower than the D50; and D50 being measured
by laser diffraction analysis on a Malvern type analyzer. [0023] 2.
A process for preparing a polyethylene in at least one continuously
stirred tank reactor, comprising the step of: polymerizing ethylene
in the presence of at least one supported metallocene catalyst, a
diluent, optionally one or more co-monomers, and optionally
hydrogen, thereby obtaining the polyethylene, [0024] wherein said
supported metallocene catalyst comprises a solid support, a
co-catalyst and at least one metallocene, [0025] wherein the solid
support has a surface area within the range of from 100 to 500
m.sup.2/g, preferably from 150 m.sup.2/g to 400 m.sup.2/g,
preferably from 200 m.sup.2/g to 350 m.sup.2/g, preferably from 200
m.sup.2/g to 300 m.sup.2/g, and preferably from 250 m.sup.2/g to
300 m.sup.2/g; and has a D50 value within the range of from 4 .mu.m
to 18 .mu.m, with D50 being defined as the particle size for which
fifty percent by weight of the particles has a size lower than the
D50; and D50 being measured by laser diffraction analysis on a
Malvern type analyzer. [0026] 3. A process for preparing a
polyethylene in at least one continuously stirred tank reactor,
comprising the step of: polymerizing ethylene in the presence of at
least one supported metallocene catalyst, a diluent, optionally one
or more co-monomers, and optionally hydrogen, thereby obtaining the
polyethylene, wherein said polyethylene at the end of said process
has a silicon content lower than 60 ppm by weight, and a D50 of at
least 100 and at most 400 .mu.m, with D50 being defined as the
particle size for which fifty percent by weight of the particles
has a size lower than the D50, as measured by sieving techniques or
optical measurements, preferably by sieving techniques. [0027] 4.
The process according to statement 3, wherein said supported
metallocene catalyst comprises a solid support, a co-catalyst and
at least one metallocene. [0028] 5. The process according to any
one of statements 1 to 4, wherein said at least one supported
metallocene catalyst comprises a silica-containing solid support,
an alumoxane, and least one metallocene. [0029] 6. The process
according to any one of statements 1 to 5, wherein said at least
one supported metallocene catalyst comprises a silica- and
titania-containing solid support, an alumoxane, and least one
metallocene. [0030] 7. The process according to statement 6,
wherein the supported catalyst system has a Ti content of from 0.1
to 10% by weight (wt %) based on the total weight of the supported
metallocene catalyst, for example from 0.5 to 5% by weight, for
example from 1.0 to 2.5% by weight. Preferably from 1.0 to 10% by
weight, more preferably from 0.5 to 10% by weight, even more
preferably from 0.5 to 5.0% by weight. Most preferably, the Ti
content is from 1.0 to 5% by weight, more preferably from 1.0 to
2.5% by weight, more preferably from 1.0 to 2.0% by weight, for
example about 1.5% by weight based on the total weight of the
supported metallocene catalyst. [0031] 8. The process according to
any one of statements 1 to 7, wherein the solid support of said at
least one supported metallocene catalyst has a particle size
distribution of a span value lower than 2.0, preferably has a span
value of at least 0.9 and at most 1.3, wherein the span is defined
as:
[0031] span = D 90 - D 10 D 50 ##EQU00001## [0032] with D90 being
defined as the particle size for which ninety percent by weight of
the particles has a size lower than the D90; [0033] with D10 being
defined as the particle size for which ten percent by weight of the
particles has a size lower than the D10; [0034] with D50 being
defined as the particle size for which fifty percent by weight of
the particles has a size lower than the D50; and [0035] with the
D90, D10 and D50 being measured by laser diffraction analysis on a
Malvern type analyzer. [0036] 9. The process according to any one
of statements 1 to 8, wherein the solid support of said at least
one supported metallocene catalyst has an average pore volume of at
least 1.0 and at most 3.0 ml/g, preferably at least 1.0 and at most
2.5 ml/g, more preferably at least 1.2 and at most 2.0 ml/g. [0037]
10. The process according to any one of statements 1 to 9, wherein
the metallocene catalyst is a compound of formula (I) or (II)
[0037] (Ar).sub.2MQ.sub.2 (I)
R''(Ar).sub.2MQ.sub.2 (II) [0038] wherein the metallocenes
according to formula (I) are non-bridged metallocenes and the
metallocenes according to formula (II) are bridged metallocenes;
[0039] wherein said metallocene according to formula (I) or (II)
has two Ar bound to M which can be the same or different from each
other; [0040] wherein Ar is an aromatic ring, group or moiety and
wherein each Ar is independently selected from the group consisting
of cyclopentadienyl, indenyl (IND), tetrahydroindenyl (THI), and
fluorenyl, wherein each of said groups may be optionally
substituted with one or more substituents each independently
selected from the group consisting of halogen, and a hydrocarbyl
having 1 to 20 carbon atoms, and wherein said hydrocarbyl
optionally contains one or more atoms selected from the group
comprising B, Si, S, O, F, and P; [0041] wherein M is a transition
metal selected from the group consisting of titanium, zirconium,
hafnium, and vanadium; and preferably is zirconium; [0042] wherein
each Q is independently selected from the group consisting of
halogen, a hydrocarboxy having 1 to 20 carbon atoms, and a
hydrocarbyl having 1 to 20 carbon atoms and wherein said
hydrocarbyl optionally contains one or more atoms selected from the
group comprising B, Si, S, O, F, and P; and [0043] wherein R'' is a
divalent group or moiety bridging the two Ar groups and selected
from the group consisting of C.sub.1-C.sub.20 alkylene, germanium,
silicon, siloxane, alkylphosphine, and an amine, and wherein said
R'' is optionally substituted with one or more substituents each
independently selected from the group consisting of halogen, a
hydrocarbyl having 1 to 20 carbon atoms, and wherein said
hydrocarbyl optionally contains one or more atoms selected from the
group comprising B, Si, S, O, F, and P. [0044] 11. The process
according to any one of statements 1 to 10, wherein the metallocene
catalyst is a compound selected from one of the following formula
(III) or (IV):
[0044] ##STR00001## [0045] wherein each R in formula (III) or (IV)
is the same or different and is selected independently from
hydrogen or XR'.sub.v in which X is chosen from Group 14 of the
Periodic Table, oxygen or nitrogen and each R' is the same or
different and is chosen from hydrogen or a hydrocarbyl of from 1 to
20 carbon atoms and v+1 is the valence of X; R'' is a structural
bridge between the two indenyl or tetrahydrogenated indenyls that
comprises a C1-C4 alkylene radical, a dialkyl germanium, silicon or
siloxane, or an alkyl phosphine or amine radical; Q is a halogen or
a hydrocarbyl radical having from 1 to 20 carbon atoms, preferably
Q is F, Cl or Br; and M is a transition metal selected from the
group consisting of titanium, zirconium, hafnium, and vanadium; and
preferably is zirconium. [0046] 12. The process according to any
one of statements 1 to 11, wherein the metallocene catalyst
comprises a bridged unsubstituted bis-indenyl and/or a bridged
unsubstituted bis-tetrahydrogenated indenyl. [0047] 13. The process
according to any one of statements 1 to 12, wherein the metallocene
catalyst comprises a bridged unsubstituted bis-tetrahydrogenated
indenyl. [0048] 14. The process according to any one of statements
1 to 13, wherein the metallocene catalyst comprises at least one
compound selected from the group comprising bis(cyclopentadienyl)
zirconium dichloride (Cp.sub.2ZrCl.sub.2), bis(cyclopentadienyl)
titanium dichloride (Cp.sub.2TiCl.sub.2), bis(cyclopentadienyl)
hafnium dichloride (Cp.sub.2HfCl.sub.2); bis(tetrahydroindenyl)
zirconium dichloride, bis(indenyl) zirconium dichloride, and
bis(n-butyl-cyclopentadienyl) zirconium dichloride;
ethylenebis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride,
ethylenebis(1-indenyl) zirconium dichloride, dimethylsilylene
bis(2-methyl-4-phenyl-inden-1-yl) zirconium dichloride,
diphenylmethylene (cyclopentadienyl)(fluoren-9-yl) zirconium
dichloride, and dimethylmethylene
[1-(4-tert-butyl-2-methyl-cyclopentadienyl)](fluoren-9-yl)
zirconium dichloride. [0049] 15. The process according to any one
of statements 1 to 14, wherein the metallocene catalyst comprises
ethylene-bis(tetrahydroindenyl)zirconium dichloride or
ethylene-bis(tetrahydroindenyl) zirconium difluoride. [0050] 16.
The process according to any one of statements 1 to 15, wherein the
solid support of said at least one supported metallocene catalyst
has a D50 ranging of from 4.0 .mu.m to 15.0 .mu.m. [0051] 17. The
process according to any one of statements 1 to 16, wherein the
co-monomer is 1-butene. [0052] 18. The process according to any one
of statements 1 to 17, wherein said diluent is selected from
hexane, isohexane, or heptane [0053] 19. The process according to
any one of statements 1 to 18, wherein said polymerization process
is performed in the presence of at least one antifouling agent.
[0054] 20. The process according to any one of statements 1 to 19,
wherein said process is performed in at least two continuously
stirred tank reactors connected in series. [0055] 21. The process
according to any one of statements 1 to 20, wherein said
polyethylene has a monomodal molecular weight distribution. [0056]
22. The process according to any one of statements 1 to 21, wherein
said polyethylene has a bimodal molecular weight distribution.
[0057] 23. The process according to any one of statements 1 to 22,
wherein the solid support of said supported metallocene catalyst is
a silica-containing support. [0058] 24. The process according to
any one of statements 1 to 23, wherein the solid support of said
supported metallocene catalyst is a silica-containing support
comprising at least 20% by weight of silica, for example at least
40% by weight, for example at least 50% by weight of silica,
preferably 100% of silica, preferably amorphous silica. [0059] 25.
The process according to any one of statements 1 to 24, wherein the
solid support of said supported metallocene catalyst is a
silica-containing support having a surface area of at least 100
m.sup.2/g, for example of at least 150 m.sup.2/g, more preferably
of at least 200 m.sup.2/g, preferably to at most 400 m.sup.2/g,
more preferably to at most 350 m.sup.2/g and more preferably to at
most 300 m.sup.2/g, for example from 100 m.sup.2/g to 500
m.sup.2/g, for example from 150 m.sup.2/g to 400 m.sup.2/g, for
example from 200 m.sup.2/g to 350 m.sup.2/g, for example from 200
m.sup.2/g to 300 m.sup.2/g, preferably from 250 m.sup.2/g to 300
m.sup.2/g. The specific surface area is measured by N.sub.2
adsorption using the well-known BET technique. [0060] 26. The
process according to any one of statements 1 to 25, wherein the
solid support of said supported metallocene catalyst is a
silica-containing support having a D50 within the range of from 3.0
to 25.0 .mu.m, preferably from 4.0 .mu.m to 23.0 .mu.m, preferably
from 4.0 .mu.m to 20.0 .mu.m, preferably from 4.0 .mu.m to 18.0
.mu.m, preferably from 5.0 .mu.m to 15.0 .mu.m, preferably from 6.0
.mu.m to 15.0 .mu.m, preferably from 7.0 .mu.m to 15.0 .mu.m.
[0061] 27. The process according to any one of statements 1 to 26,
wherein the solid support has a surface area within the range of
from 100 to 400 m.sup.2/g, preferably from 100 m.sup.2/g to 350
m.sup.2/g, preferably from 100 m.sup.2/g to 300 m.sup.2/g,
preferably from 200 m.sup.2/g to 300 m.sup.2/g, and preferably from
250 m.sup.2/g to 300 m.sup.2/g; and has a D50 value within the
range of from 5.0 .mu.m to 25.0 .mu.m, preferably from 6.0 .mu.m to
20.0 .mu.m, preferably from 7.0 .mu.m to 20.0 .mu.m, preferably
from 8.0 .mu.m to 20.0 .mu.m, preferably from 8.0 .mu.m to 15.0
.mu.m. [0062] 28. The process according to any one of statements 1
to 27, wherein the solid support of said supported metallocene
catalyst is a silica-containing support having an average pore
volume of at least 1.0 and at most 3.0 ml/g, preferably at least
1.0 and at most 2.5 ml/g, more preferably at least 1.2 and at most
2.0 ml/g. [0063] 29. The process according to any one of statements
1 to 28, wherein said at least one supported metallocene catalyst
is comprising a silica- and titania-containing support comprising
an alumoxane at and least one metallocene; obtainable by a process
comprising the following step: a) titanating a silica-containing
support having a specific surface area of from 100 m.sup.2/g to 500
m.sup.2/g, preferably 150 to 400 m.sup.2/g, more preferably 200
m.sup.2/g to 350 m.sup.2/g, and having a D50 of at least 3.0 .mu.m
and at most 25.0 .mu.m; preferably from 4.0 .mu.m to 23.0 .mu.m,
preferably from 4.0 .mu.m to 20.0 .mu.m, preferably from 4.0 .mu.m
to 18.0 .mu.m, preferably from 4.0 .mu.m to 15.0 .mu.m; by
impregnating the support with a titanium compound to form a
titanated silica-containing catalyst support; wherein the supported
catalyst system further comprises an alumoxane and a metallocene.
[0064] 30. The process according to statement 29, wherein the
titanium compound is selected from R.sup.3.sub.xTi(OR.sup.4).sub.y
and/or (R.sup.3O).sub.xTi(OR.sup.4).sub.y, wherein R.sup.3 and
R.sup.4 are the same or different and are selected from hydrocarbyl
groups containing from 1 to 12 carbon, halogens, preferably
chlorine and fluorine, and hydrogen, and wherein x is 0 to 4, y is
0 to 4 and y+x equals 4. [0065] 31. The process according to
statement 29 or 30, wherein the titanium compound is one or more
compounds of formula Ti(OR.sup.5).sub.4 wherein each R.sup.5 is the
same or different and can be an alkyl or cycloalkyl group each
having from 3 to 5 carbon atoms, and mixtures thereof. [0066] 32.
The process according to any one of statements 29 to 31, wherein
the titanium compound is selected from the group comprising
Ti(OC.sub.4H.sub.9).sub.4, Ti(OC.sub.3H.sub.7).sub.4 and mixtures
thereof. [0067] 33. The process according to any one of statements
29 to 32, wherein the titanium compound is a mixture comprising
Ti(OC.sub.4H.sub.9).sub.4 and Ti(OC.sub.3H.sub.7).sub.4. [0068] 34.
The process according to any one of statements 1 to 33, wherein
said process is performed in at least two continuously stirred tank
reactors connected in series, under slurry conditions. [0069] 35.
The process according to any one of statements 1 to 34, wherein
said polymerization process is performed in the presence of at
least one antifouling agent at a level of from 0.1 to 50 ppm,
preferably from 1.0 to 20 ppm, preferably from 1.0 to 10.0 ppm,
preferably from 2.0 to 6.0 ppm, preferably from 2.0 to 5.0 ppm.
[0070] 36. The process according to any one of statements 1 to 35,
wherein said polyethylene at the end of said process has a D50 of
at least 100 and at most 400 .mu.m, preferably at most 350 .mu.m,
preferably at most 300 .mu.m, preferably at most 250 .mu.m. [0071]
37. The process according to any one of statements 1 to 36, wherein
said polyethylene at the end of said process has a silicon content
lower than 60 ppm by weight, preferably lower than 55 ppm by
weight, more preferably lower than 50 ppm by weight, for example
from 5 to 60 ppm by weight, for example from 5 to 55 ppm by weight,
for example from 5 to 50 ppm by weight. [0072] 38. The process
according to any one of statements 1 to 37, wherein said
polyethylene at the end of said process has a D50 of at least 100
and at most 400 .mu.m, and a silicon content lower than 60 ppm by
weight; for example a D50 of at least 100 and at most 350 .mu.m,
preferably of at least 100 and at most 300 .mu.m, preferably of at
least 100 at most 250 .mu.m, and a silicon content lower than 60
ppm by weight, preferably lower than 55 ppm by weight, more
preferably lower than 50 ppm by weight. [0073] 39. A polyethylene
prepared according to the process of any one of statements 1 to 38.
[0074] 40. A polyethylene prepared in at least one CSTR in the
presence of at least one supported metallocene catalyst, wherein
said polyethylene has a D50 ranging from 100 to 400 .mu.m, with D50
being defined as the particle size for which fifty percent by
weight of the particles has a size lower than the D50. Preferably,
the polyethylene has a D50 of at most 350 .mu.m, preferably at most
300 .mu.m, preferably at most 250 .mu.m. [0075] 41. A polyethylene
prepared in at least one CSTR in the presence of at least one
supported metallocene catalyst, wherein said polyethylene has a Si
content of at most 60 ppm by weight, for example at most 55 ppm by
weight, for example at most 50 ppm by weight, preferably from 5 to
60 ppm by weight, for example from 5 to 55 ppm by weight, for
example from 5 to 50 ppm by weight. [0076] 42. The polyethylene
according to any one of statements 39 to 41, wherein said
polyethylene has a bimodal molecular weight distribution. [0077]
43. The polyethylene according to any one of statements 39 to 42,
wherein said polyethylene has a D50 ranging from 100 to 400 .mu.m,
and a Si content of at most 60 ppm by weight. [0078] 44. The
polyethylene according to any one of statements 39 to 43, wherein
the polyethylene has a D50 of at most 350 .mu.m, for example at
most 300 .mu.m, for example at most 250 .mu.m, and a Si content of
at most 60 ppm by weight, for example at most 55 ppm by weight, for
example at most 50 ppm by weight, for example from 5 to 60 ppm by
weight, for example from 5 to 55 ppm by weight, for example from 5
to 50 ppm by weight. [0079] 45. The polyethylene according to any
one of statements 39 to 44, wherein polyethylene has a density of
at least 940 g/cm.sup.3, as measured according to ASTM D-1505 at
23.degree. C. [0080] 46. An article comprising a polyethylene
prepared according to the process of any one of the statements 1 to
38, or a polyethylene according to any one of statements 39 to 45.
[0081] 47. The article according to statement 46, wherein said
article is selected from the group comprising films, pipes,
preferably pipes PERT (polyethylene of Raised Temperature
resistance), injection molded articles, injection stretch blow
molded articles, rotomoulded articles, caps and closures, fibers,
sheets, containers, and foams.
[0082] The present invention provides a process for preparing a
polyethylene in at least one continuously stirred tank reactor,
comprising the step of: polymerizing ethylene in the presence of at
least one supported metallocene catalyst, a diluent, optionally one
or more co-monomers, and optionally hydrogen, thereby obtaining the
polyethylene, wherein said supported metallocene catalyst comprises
a solid support, a co-catalyst and at least one metallocene,
wherein the solid support of said supported metallocene catalyst
has a surface area within the range of from 100 to 500 m.sup.2/g,
and has a D50 value within the range of from 3 .mu.m to 25 .mu.m,
preferably from 4 .mu.m to 18 .mu.m, for example from 4 .mu.m to 15
.mu.m, and with D50 being defined as the particle size for which
fifty percent by weight of the particles has a size lower than the
D50; and D50 being measured by laser diffraction analysis on a
Malvern type analyze.
[0083] The process comprises polymerizing ethylene in the presence
of at least one supported metallocene catalyst, a diluent,
optionally one or more co-monomers, and optionally hydrogen.
[0084] As used herein, the term "catalyst" refers to a substance
that causes a change in the rate of a polymerization reaction. In
the present invention, it is especially applicable to catalysts
suitable for the polymerization of ethylene to polyethylene. The
present invention especially relates to metallocene catalysts, in
particular to supported metallocene catalysts.
[0085] The metallocene catalyst refers to any transition metal
complexes consisting of metal atoms bonded to one or more ligands.
The metallocene catalysts are compounds of Group IV transition
metals of the Periodic Table such as titanium, zirconium, hafnium,
etc., and have a coordinated structure with a metal compound and
ligands composed of one or two groups of cyclopentadienyl, indenyl,
fluorenyl or their derivatives. The structure and geometry of the
metallocene can be varied to adapt to the specific need of the
producer depending on the desired polymer. Metallocenes comprise a
single metal site, which allows for more control of branching and
molecular weight distribution of the polymer. Monomers are inserted
between the metal and the growing chain of polymer.
[0086] In one embodiment of the present invention, the metallocene
catalyst is a compound of formula (I) or (II)
(Ar).sub.2MQ.sub.2 (I);
R''(Ar).sub.2MQ.sub.2 (II),
[0087] wherein the metallocenes according to formula (I) are
non-bridged metallocenes and the metallocenes according to formula
(II) are bridged metallocenes;
[0088] wherein said metallocene according to formula (I) or (II)
has two Ar bound to M which can be the same or different from each
other;
[0089] wherein Ar is an aromatic ring, group or moiety and wherein
each Ar is independently selected from the group consisting of
cyclopentadienyl, indenyl (IND), tetrahydroindenyl (THI), and
fluorenyl, wherein each of said groups may be optionally
substituted with one or more substituents each independently
selected from the group consisting of halogen, and a hydrocarbyl
having 1 to 20 carbon atoms, and wherein said hydrocarbyl
optionally contains one or more atoms selected from the group
comprising B, Si, S, O, F, and P;
[0090] wherein M is a transition metal selected from the group
consisting of titanium, zirconium, hafnium, and vanadium; and
preferably is zirconium;
[0091] wherein each Q is independently selected from the group
consisting of halogen, a hydrocarboxy having 1 to 20 carbon atoms,
and a hydrocarbyl having 1 to 20 carbon atoms and wherein said
hydrocarbyl optionally contains one or more atoms selected from the
group comprising B, Si, S, O, F, and P; and wherein R'' is a
divalent group or moiety bridging the two Ar groups and selected
from the group consisting of C.sub.1-C.sub.20 alkylene, germanium,
silicon, siloxane, alkylphosphine, and an amine, and wherein said
R'' is optionally substituted with one or more substituents each
independently selected from the group consisting of halogen, a
hydrocarbyl having 1 to 20 carbon atoms, and wherein said
hydrocarbyl optionally contains one or more atoms selected from the
group comprising B, Si, S, O, F, and P. As used herein, the term
"hydrocarbyl having 1 to 20 carbon atoms" refers to a moiety
selected from the group comprising a linear or branched
C.sub.1-C.sub.20 alkyl; C.sub.3-C.sub.20 cycloalkyl;
C.sub.6-C.sub.20 aryl; C.sub.7-C.sub.20 alkylaryl and
C.sub.7-C.sub.20 arylalkyl, or any combinations thereof. Exemplary
hydrocarbyl groups are methyl, ethyl, propyl, butyl, amyl, isoamyl,
hexyl, isobutyl, heptyl, octyl, nonyl, decyl, cetyl, 2-ethylhexyl,
and phenyl.
[0092] As used herein, the term "hydrocarboxy having 1 to 20 carbon
atoms" refers to a moiety with the formula hydrocarbyl-O--, wherein
the hydrocarbyl has 1 to 20 carbon atoms as described herein.
Preferred hydrocarboxy groups are selected from the group
comprising alkyloxy, alkenyloxy, cycloalkyloxy or aralkoxy groups,
preferably methoxy, ethoxy, butoxy and amyloxy.
[0093] As used herein, the term "alkyl", by itself or as part of
another substituent, refers to straight or branched saturated
hydrocarbon group joined by single carbon-carbon bonds having 1 or
more carbon atom, for example 1 to 12 carbon atoms, for example 1
to 6 carbon atoms, for example 1 to 4 carbon atoms. When a
subscript is used herein following a carbon atom, the subscript
refers to the number of carbon atoms that the named group may
contain. Thus, for example, C.sub.1-12alkyl means an alkyl of 1 to
12 carbon atoms. Examples of alkyl groups are methyl, ethyl,
propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl,
2-methylbutyl, pentyl and its chain isomers, hexyl and its chain
isomers, heptyl and its chain isomers, octyl and its chain isomers,
nonyl and its chain isomers, decyl and its chain isomers, undecyl
and its chain isomers, dodecyl and its chain isomers. Alkyl groups
have the general formula C.sub.nH.sub.2n+1.
[0094] As used herein, the term "cycloalkyl", by itself or as part
of another substituent, refers to a saturated or partially
saturated cyclic alkyl radical. Cycloalkyl groups have the general
formula C.sub.nH.sub.2n-1. When a subscript is used herein
following a carbon atom, the subscript refers to the number of
carbon atoms that the named group may contain. Thus, examples of
C.sub.3-6cycloalkyl include cyclopropyl, cyclobutyl, cyclopentyl,
or cyclohexyl.
[0095] As used herein, the term "aryl", by itself or as part of
another substituent, refers to a radical derived from an aromatic
ring, such as phenyl, naphthyl, indanyl, or
1,2,3,4-tetrahydro-naphthyl. When a subscript is used herein
following a carbon atom, the subscript refers to the number of
carbon atoms that the named group may contain.
[0096] As used herein, the term "alkylaryl", by itself or as part
of another substituent, refers to refers to an aryl group as
defined herein, wherein a hydrogen atom is replaced by an alkyl as
defined herein. When a subscript is used herein following a carbon
atom, the subscript refers to the number of carbon atoms that the
named group or subgroup may contain.
[0097] As used herein, the term "arylalkyl", by itself or as part
of another substituent, refers to an alkyl group as defined herein,
wherein a hydrogen atom is replaced by a aryl as defined herein.
When a subscript is used herein following a carbon atom, the
subscript refers to the number of carbon atoms that the named group
may contain. Examples of C.sub.6-10arylC.sub.1-6alkyl radicals
include benzyl, phenethyl, dibenzylmethyl, methylphenylmethyl,
3-(2-naphthyl)-butyl, and the like.
[0098] As used herein, the term "alkylene", by itself or as part of
another substituent, refers to alkyl groups that are divalent,
i.e., with two single bonds for attachment to two other groups.
Alkylene groups may be linear or branched and may be substituted as
indicated herein. Non-limiting examples of alkylene groups include
methylene (--CH.sub.2--), ethylene (--CH.sub.2--CH.sub.2--),
methylmethylene (--CH(CH.sub.3)--), 1-methyl-ethylene
(--CH(CH.sub.3)--CH.sub.2--), n-propylene
(--CH.sub.2--CH.sub.2--CH.sub.2--), 2-methylpropylene
(--CH.sub.2--CH(CH.sub.3)--CH.sub.2--), 3-methylpropylene
(--CH.sub.2--CH.sub.2--CH(CH.sub.3)--), n-butylene
(--CH.sub.2--CH.sub.2--CH.sub.2--CH.sub.2--), 2-methylbutylene
(--CH.sub.2--CH(CH.sub.3)--CH.sub.2--CH.sub.2--), 4-methylbutylene
(--CH.sub.2--CH.sub.2--CH.sub.2--CH(CH.sub.3)--), pentylene and its
chain isomers, hexylene and its chain isomers, heptylene and its
chain isomers, octylene and its chain isomers, nonylene and its
chain isomers, decylene and its chain isomers, undecylene and its
chain isomers, dodecylene and its chain isomers. When a subscript
is used herein following a carbon atom, the subscript refers to the
number of carbon atoms that the named group may contain. For
example, C.sub.1-C.sub.20 alkylene refers to an alkylene having
between 1 and 20 carbon atoms. Exemplary halogen atoms include
chlorine, bromine, fluorine and iodine, wherein fluorine and
chlorine are preferred.
[0099] Preferably, the metallocene comprises a bridged bis-indenyl
and/or a bridged bis-tetrahydrogenated indenyl catalyst component.
More preferably, the metallocene is selected from one of the
following formula (III) or (IV):
##STR00002##
[0100] wherein each R is the same or different and is selected
independently from hydrogen or XR'v in which X is chosen from Group
14 of the Periodic Table (preferably carbon), oxygen or nitrogen
and each R' is the same or different and is chosen from hydrogen or
a hydrocarbyl of from 1 to 20 carbon atoms and v+1 is the valence
of X, preferably R is a hydrogen, methyl, ethyl, n-propyl,
iso-propyl, n-butyl, tert-butyl group; R'' is a structural bridge
between the two indenyl or tetrahydrogenated indenyls to impart
stereorigidity that comprises a C.sub.1-C.sub.4 alkylene radical, a
dialkyl germanium, silicon or siloxane, or an alkyl phosphine or
amine radical; Q is a hydrocarbyl radical having from 1 to 20
carbon atoms or a halogen, preferably Q is F, Cl or Br; and M is a
transition metal selected from the group consisting of titanium,
zirconium, hafnium, and vanadium; and preferably is zirconium.
[0101] Each indenyl or tetrahydro indenyl component may be
substituted with R in the same way or differently from one another
at one or more positions of either of the fused rings. Each
substituent is independently chosen.
[0102] If the cyclopentadienyl ring is substituted, its substituent
groups must not be so bulky so as to affect coordination of the
olefin monomer to the metal M. Any substituents XR'v on the
cyclopentadienyl ring are preferably methyl. More preferably, at
least one and most preferably both cyclopentadienyl rings are
unsubstituted.
[0103] In a particularly preferred embodiment the metallocene
catalyst comprises a bridged unsubstituted bis-indenyl and/or a
bridged unsubstituted bis-tetrahydrogenated indenyl.
[0104] In another particularly preferred embodiment the metallocene
catalyst comprises a bridged unsubstituted bis-tetrahydrogenated
indenyl.
[0105] Illustrative examples of metallocene catalysts comprise but
are not limited to bis(cyclopentadienyl) zirconium dichloride
(Cp.sub.2ZrCl.sub.2), bis(cyclopentadienyl) titanium dichloride
(Cp.sub.2TiCl.sub.2), bis(cyclopentadienyl) hafnium dichloride
(Cp.sub.2HfCl.sub.2); bis(tetrahydroindenyl) zirconium dichloride,
bis(indenyl) zirconium dichloride, and
bis(n-butyl-cyclopentadienyl) zirconium dichloride;
ethylenebis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride,
ethylenebis(1-indenyl) zirconium dichloride, dimethylsilylene
bis(2-methyl-4-phenyl-inden-1-yl) zirconium dichloride,
diphenylmethylene (cyclopentadienyl) (fluoren-9-yl) zirconium
dichloride, and dimethylmethylene
[1-(4-tert-butyl-2-methyl-cyclopentadienyl)](fluoren-9-yl)
zirconium dichloride. Most preferably the metallocene is
ethylene-bis(tetrahydroindenyl)zirconium dichloride or
ethylene-bis(tetrahydroindenyl) zirconium difluoride.
[0106] The metallocene catalysts used herein are provided on a
solid support. The support can be an inert organic or inorganic
solid, which is chemically unreactive with any of the components of
the metallocene catalyst.
[0107] Suitable support materials for the supported catalyst
include solid inorganic oxides, such as silica, alumina, magnesium
oxide, titanium oxide, thorium oxide, as well as mixed oxides of
silica and one or more Group 2 or 13 metal oxides, such as
silica-magnesia and silica-alumina mixed oxides. Examples of such
mixed oxides are the silica-aluminas. Most preferred is a silica
compound.
[0108] Preferred supports are silica-containing supports comprising
at least 20% by weight of silica, for example at least 40% by
weight, for example at least 50% by weight of amorphous silica. The
silica-containing support may also contain one or more of alumina,
magnesia, zirconia and the like.
[0109] Preferably the support is a silica support i.e. essentially
100% by weight of silica, or a silica-titania, or a silica-alumina
support. In the case of silica-alumina supports, the support
preferably comprises at most 15% by weight of alumina.
[0110] According to the invention, the solid support of the
supported metallocene catalyst is a support having a surface area
within the range of 100 to 500 m.sup.2/g, preferably a porous
support having a surface area within the range of 100 to 500
m.sup.2/g, preferably a porous silica support having a surface area
within the range of 100 to 500 m.sup.2/g. Suitable silica support
are, for example, amorphous silica having a surface area of at
least 100 m.sup.2/g and at most 500 m.sup.2/g. Preferably of at
least 150 m.sup.2/g, more preferably of at least 200 m.sup.2/g,
preferably to at most 400 m.sup.2/g, more preferably to at most 350
m.sup.2/g and more preferably to at most 300 m.sup.2/g, for example
from 100 m.sup.2/g to 500 m.sup.2/g, for example from 150 m.sup.2/g
to 400 m.sup.2/g, for example from 200 m.sup.2/g to 350 m.sup.2/g,
for example from 200 m.sup.2/g to 300 m.sup.2/g, preferably from
250 m.sup.2/g to 300 m.sup.2/g. The specific surface area is
measured by N.sub.2 adsorption using the well-known BET technique.
It is to be understood that the surface area referred herein, it
the surface area measured for the solid support without any
catalyst activator (co-catalyst).
[0111] For example, the surface area, along with pore volume, can
be measured by nitrogen porosimetry using an Autosorb 6 analyzer
(Quantachrome Corporation, Boynton Beach, Fla., USA). Samples are
first outgassed at 350.degree. C. for 4 hours on the instrument's
outgassing station prior to measurement. The sample tube
(containing the outgassed sample) is transferred to the analysis
station, submerged in liquid nitrogen and a nitrogen isotherm
determined. A surface area is calculated using BET theory taking
data points in the P/Po range 0.05 to 0.30 (P/P0=relative
pressure). A pore volume measurement is recorded at P/Po of 0.98 on
the adsorption leg.
[0112] According to the invention, the support has a D50 value
within the range of from 3 .mu.m to 25 .mu.m, with D50 being
defined as the particle size for which fifty percent by weight of
the particles has a size lower than the D50. In some embodiments,
the support has a D50 of at most 23 .mu.m, preferably of at most 20
.mu.m, preferably of at most 18 .mu.m, preferably of at most 15
.mu.m. In some preferred embodiments, the support is an amorphous
silica having a D50 of at least 3.0 .mu.m, preferably at least 4.0
.mu.m, preferably at least 4.5 .mu.m, most preferably at least 4.0
and at most 15.0 .mu.m. Preferably, said support has a D50 within
the range of from 4.0 .mu.m to 23.0 .mu.m, preferably from 4.0
.mu.m to 20.0 .mu.m, preferably from 4.0 .mu.m to 18.0 .mu.m,
preferably from 4.0 .mu.m to 15.0 .mu.m. It is to be understood
that the solid support D50 referred herein is the D50 measured for
the solid support without any catalyst activator (co-catalyst).
[0113] The measurement of the particle size can be made according
to the International Standard ISO 13320:2009 ("Particle size
analysis--Laser diffraction methods"). For example, the D50 can be
measured by laser diffraction analysis. Malvern Instruments' laser
diffraction systems may advantageously be used. Preferably, the
support particle size is measured by laser diffraction analysis on
a Malvern type analyzer. The particle size may be measured by laser
diffraction analysis on a Malvern type analyzer after having put
the supported catalyst in suspension in cyclohexane. Suitable
Malvern systems include the Malvern 2000, Malvern MasterSizer (such
as Mastersizer S), Malvern 2600 and Malvern 3600 series. Such
instruments together with their operating manual meet or even
exceed the requirements set-out within the ISO 13320 Standard. The
Malvern MasterSizer (such as Mastersizer S) may also be useful as
it can more accurately measure the D50 towards the lower end of the
range e.g. for average particle sizes of less 8 .mu.m, by applying
the theory of Mie, using appropriate optical means. In some
preferred embodiments, the support has a D50 of at most 25 .mu.m,
preferably of at most 23 .mu.m, preferably of at most 20 .mu.m,
preferably of at most 18 .mu.m, preferably of at most 15 .mu.m,
with D50 being defined as the particle size for which fifty percent
by weight of the particles has a size lower than the D50, as
measured according to the International Standard ISO 13320:2009
("Particle size analysis--Laser diffraction methods") with the
Mastersizer S by applying the theory of Mie. A non-limiting example
of a suitable silica support having a D50 value within the range of
from 3 .mu.m to 25 .mu.m, can be for example silica support sold by
PQ Corporation under the name PD-10001 having a D50 of about 12.5
.mu.m and a surface area of 285 m.sup.2/g.
[0114] Such a small catalyst particle size improves degassing and
decreases fouling. Also, small catalyst particle size improves
downstream processes. Furthermore, small catalyst particle size
results in improved polyethylene properties, and therefore also
articles prepared from such improved polyethylene exhibit also
better properties.
[0115] In an embodiment, the support of the supported metallocene
catalyst is a support having an average pore volume within the
range of 1.0 to 3.0 ml/g, and preferably a porous silica support
having an average pore volume within the range of 1.0 to 2.5 ml/g.
Supports with a pore volume of 1.2 to 2.0 ml/g are preferred. Pore
volume is measured by N.sub.2 desorption using the BJH method for
pores with a diameter of less than 1000 .ANG.. In some preferred
embodiments, the support is an amorphous silica having an average
pore volume of at least 1.0 and at most 3.0 ml/g, preferably at
least 1.0 and at most 2.5 ml/g, more preferably at least 1.2 and at
most 2.0 ml/g. Supports with too small porosity may result in a
loss of melt index potential and in a lower activity.
[0116] In a preferred embodiment, said solid support is a silica-
and titania-containing support. Preferably said silica- and
titania-containing support has a surface area within the range of
100 to 500 m.sup.2/g. Preferably of at least 150 m.sup.2/g, more
preferably of at least 200 m.sup.2/g, preferably to at most 400
m.sup.2/g, more preferably to at most 350 m.sup.2/g and more
preferably to at most 300 m.sup.2/g, for example from 100 m.sup.2/g
to 500 m.sup.2/g, for example from 150 m.sup.2/g to 400 m.sup.2/g,
for example from 200 m.sup.2/g to 350 m.sup.2/g, for example from
200 m.sup.2/g to 300 m.sup.2/g, preferably from 250 m.sup.2/g to
300 m.sup.2/g.
[0117] Preferably said silica- and titania-containing support has a
D50 value within the range of from 3 .mu.m to 25 .mu.m. Preferably,
the silica- and titania-containing support has a D50 of at most 23
.mu.m, preferably of at most 20 .mu.m, preferably of at most 18
.mu.m, preferably of at most 15 .mu.m. Preferably, the silica- and
titania-containing support has a D50 of at least 3.0 .mu.m,
preferably at least 4.0 .mu.m, preferably at least 4.5 .mu.m, most
preferably at least 4.0 and at most 15.0 .mu.m.
[0118] Preferably said silica- and titania-containing support has
an average pore volume of at least 1.0 and at most 3.0 ml/g,
preferably at least 1.0 and at most 2.5 ml/g, more preferably at
least 1.2 and at most 2.0 ml/g.
[0119] In a preferred embodiment, said silica- and
titania-containing support can be prepared by a process comprising
the following step: titanating a silica-containing support having a
specific surface area of from 100 m.sup.2/g to 500 m.sup.2/g,
preferably 150 to 400 m.sup.2/g, more preferably 200 m.sup.2/g to
350 m.sup.2/g, and having a D50 of at least 3.0 .mu.m and at most
25.0 .mu.m; preferably from 5.0 .mu.m to 23.0 .mu.m, preferably
from 5.0 .mu.m to 20.0 .mu.m, preferably from 5.0 .mu.m to 18.0
.mu.m, preferably from 5.0 .mu.m to 15.0 .mu.m; by impregnating the
support with a titanium compound, preferably of the general formula
selected from R.sup.3.sub.xTi(OR.sup.4).sub.y and
(R.sup.3O).sub.xTi(OR.sup.4).sub.y, wherein R.sup.3 and R.sup.4 are
the same or different and are selected from hydrocarbyl groups
containing from 1 to 12 carbon, halogens, preferably chlorine and
fluorine, and hydrogen, and wherein x is 0 to 4, y is 0 to 4 and
y+x equals 4; to form a titanated silica-containing catalyst
support. In some preferred embodiments, the silica-containing
support has an average pore volume of at least 1.0 and at most 3.0
ml/g, preferably at least 1.0 and at most 2.5 ml/g, more preferably
at least 1.2 and at most 2.0 ml/g. The silica-containing support
can be commercially available as described herein above, or can be
prepared by various known techniques such as but not limited to
gelification, precipitation and/or spray-drying.
[0120] Preferably, the silica-containing support is loaded with one
or more titanium compounds selected from
R.sup.3.sub.xTi(OR.sup.4).sub.y and
(R.sup.3O).sub.xTi(OR.sup.4).sub.y, wherein R.sup.3 and R.sup.4 are
the same or different and are selected from hydrocarbyl groups
containing from 1 to 12 carbon, halogens, preferably chlorine and
fluorine, and hydrogen, and wherein x is 0 to 4, y is 0 to 4 and
y+x equals 4. The titanium compound is preferably selected from the
group consisting of tetraalkoxides of titanium having the general
formula Ti(OR.sup.5).sub.4 wherein each R.sup.5 is the same or
different and can be an alkyl or cycloalkyl group each having from
3 to 5 carbon atoms, and mixtures thereof.
[0121] The titanium compound(s) with which the support is
impregnated is more preferably selected from alkyl titanates,
preferably selected from e.g. Ti(OC.sub.4H.sub.9).sub.4,
Ti(OC.sub.3H.sub.7).sub.4. More preferably a mixture of alkyl
titanates are used e.g. a mixture of Ti(OC.sub.4H.sub.9).sub.4 and
Ti(OC.sub.3H.sub.7).sub.4. Most preferably the mixture has a weight
ratio of 20/80 of Ti(OC.sub.4H.sub.9).sub.4 to
Ti(OC.sub.3H.sub.7).sub.4. The impregnation of the support with
alkyl titanate is preferably performed by introducing the titanium
compound(s) in a suspension in a diluent such as an organic solvent
e.g. hexane or iso-hexane, or dissolved in an aqueous solvent. The
suspension is preferably added drop-wise to the support. The
suspension is then mixed preferably for at least 1 hour, more
preferably at least 2 hours.
[0122] In an embodiment, the final amount of titanium present (the
Ti content) in the supported catalyst is at least 0.1% by weight
based on the total weight of the supported metallocene catalyst.
The resulting supported catalyst system preferably has a Ti content
of from 0.1 to 12% by weight, preferably from 0.1 to 10% by weight,
more preferably from 0.5 to 10% by weight, for example from 1.0 to
10% by weight, for example from 0.5 to 5.0% by weight. Most
preferably, the Ti content is from 1.0 to 5% by weight, more
preferably from 1.0 to 2.5% by weight, more preferably from 1.0 to
2.0% by weight, for example about 1.5% by weight based on the total
weight of the supported metallocene catalyst.
[0123] This process may further comprise the step of drying the
Ti-impregnated catalyst support.
[0124] The support is preferably dried after titanation, preferably
by heating to a temperature of from at least 100.degree. C.,
preferably of at least 250.degree. C., more preferably of at least
270.degree. C. This step generally lasts for at least 1 hour, more
preferably at least 2 hours, most preferably at least 4 hours. The
drying can take place in an atmosphere of dry and inert gas and/or
air, preferably nitrogen. The drying may be carried out in a
fluidized bed.
[0125] After impregnation and optional drying, the titanated
catalyst support can be stored under a dry and inert atmosphere,
for example, nitrogen, at ambient (room) temperature.
[0126] In another embodiment, said silica- and titania-containing
support can be prepared by a process comprising the following step:
gelification (i.e. co-precipitation) of a silica precursor with a
titanium precursor in solution. The silica precursor can also be
selected from one or more of the group having the general formula
R.sup.1.sub.nSi(OR.sup.2).sub.m or
(R.sup.1O).sub.nSi(OR.sup.2).sub.m, wherein R.sup.1 and R.sup.2 are
the same or different and are selected from hydrocarbyl groups
comprising from 1 to 12 carbon, halogens and hydrogen, and wherein
n is 0 to 4, m is 0 to 4 and m+n equals 4.
[0127] The titanium precursor can be co-precipitated in any form
from which it is subsequently convertible to titanium oxide in the
gel. Compounds suitable include inorganic and organic compounds of
titanium such as halides, nitrates, sulfates, oxalates, alkyl
titanates, alkoxides, oxides, etc. Preferred titanium compounds are
the same as those described for the impregnation process. The
co-precipitation of the titanium precursor and the silica precursor
can be performed in solution, preferably in an acidic or basic
environment. The co-precipitated support of the catalyst can be
obtained using the following steps: co-precipitating precursors of
titania and silica in solution in order to generate a gel; aging
the gel; washing the gel to remove undesirable salts; drying the
gel to obtain the co-precipitated silica and titania containing
support. The co-precipitated support of the supported catalyst
system can be prepared by first forming a gel by mixing an aqueous
solution of the silica precursor with a solution of the titania
precursor in a strong acid, e.g. such as sulphuric acid, this
mixing being done under suitable conditions of agitation. The
concentration of the silica-titania in the gel which is formed can
be in the range of between 0.1 to 12% by weight. In an embodiment,
the pH of the gel is from 3 to 9. A wide range of mixing
temperatures can be employed, this range can be from above
0.degree. C. to around 80.degree. C. After gelling, the mixture can
be aged. This can be carried out at temperatures within the range
of about 20.degree. C. to less than 100.degree. C. Aging times of
at least 10 minutes can be used, for example at least one hour.
Following the aging, the gel can be agitated to produce a slurry
which can be washed several times with, for example, water and for
example, with either an ammonium salt solution or dilute acid to
reduce the alkali metal content (the undesirable salts) in the gel
to for example less than about 0.1 weight percent. While various
ammonium salts and dilute acid solutions can be employed, the
preferred ammonium salts are those, such as ammonium nitrate and
ammonium salts of organic acids, which decompose and volatilize
upon subsequent drying. Water is removed from the gel in any
suitable manner and for example by washing with a normally liquid
organic compound which is soluble in water, or by azeotropic
distillation employing an organic compound e.g. ethyl acetate.
Remaining solvents can be removed by drying, for example in air, at
least 110.degree. C., preferably at least 150.degree. C., more
preferably at least 200.degree. C. This step generally lasts for at
least 1 hour. The drying can take place in an atmosphere of dry and
inert gas and/or air, such as nitrogen. The drying may be carried
out in a fluidized bed. The drying can be performed by spray drying
in order to have co-precipitated silica and titania containing
support having a D50 ranging from 3 .mu.m to 25 .mu.m.
[0128] The supported metallocene catalyst is activated with a
co-catalyst. The co-catalyst, which activates the metallocene
catalyst component, can be any co-catalyst known for this purpose
such as an aluminium-containing co-catalyst, a boron-containing
co-catalyst or a fluorinated catalyst. The aluminium-containing
co-catalyst may comprise an alumoxane, an alkyl aluminium, a Lewis
acid and/or a fluorinated catalytic support.
[0129] In an embodiment, alumoxane is used as an activating agent
for the supported metallocene catalyst. As used herein, the term
"alumoxane" and "aluminoxane" are used interchangeably, and refer
to a substance, which is capable of activating the metallocene
catalyst. In an embodiment, alumoxanes comprise oligomeric linear
and/or cyclic alkyl alumoxanes. In a further embodiment, the
alumoxane has formula (V) or (VI)
R.sup.a--(Al(R.sup.a)--O).sub.x--AlR.sup.a.sub.2 (V) for
oligomeric, linear alumoxanes; or (--Al(R.sup.a)--O--).sub.y (VI)
for oligomeric, cyclic alumoxanes
[0130] wherein x is 1-40, and preferably 10-20;
[0131] wherein y is 3-40, and preferably 3-20; and
[0132] wherein each R.sup.a is independently selected from a
C.sub.1-C.sub.8alkyl, and preferably is methyl. In a preferred
embodiment, the alumoxane is methylalumoxane (MAO).
[0133] In a preferred embodiment, the metallocene catalyst is a
supported metallocene-alumoxane catalyst comprising a metallocene
and an alumoxane which are bound on a porous silica support.
Preferably, the metallocene catalyst is a bridged bis-indenyl
catalyst and/or a bridged bis-tetrahydrogenated indenyl
catalyst.
[0134] One or more aluminiumalkyl represented by the formula
AlR.sup.b.sub.x can be used as additional co-catalyst, wherein each
R.sup.b is the same or different and is selected from halogens or
from alkoxy or alkyl groups having from 1 to 12 carbon atoms and x
is from 1 to 3. Non-limiting examples are Tri-Ethyl Aluminum
(TEAL), Tri-Iso-Butyl Aluminum (TIBAL), Tri-Methyl Aluminum (TMA),
and Methyl-Methyl-Ethyl Aluminum (MMEAL). Especially suitable are
trialkylaluminiums, the most preferred being triisobutylaluminium
(TIBAL) and triethylaluminum (TEAL).
[0135] The treatment of the catalyst support with the alumoxane can
be carried out according to any known method known by the person
skilled in the art. Advantageously, the alumoxane, preferably MAO,
is mixed in an inert diluent/solvent, preferably toluene, with the
catalyst support. Alumoxane deposition preferably occurs at a
temperature between 60.degree. C. to 120.degree. C., more
preferably 80.degree. C. to 120.degree. C., most preferably
100.degree. C. to 120.degree. C. The amount of MAO is calculated to
reach the desired aluminium loading.
[0136] The process may further comprise the following step:
treating the solid support with a metallocene.
[0137] The catalyst support is treated with a metallocene either
during treatment with the catalyst activating agent (1-pot method)
or thereafter. Any metallocene known in the art can be applied,
including a mixture of different metallocenes. Suitable metallocene
have been described herein above.
[0138] The support is treated with the metallocene, advantageously
by mixing the desired metallocene(s) with the MAO-modified support.
Preferably mixing occurs at room temperature for a duration of at
least 15 min, preferably at least 1 hour, more preferably at least
2 hours.
[0139] In a particular embodiment, the molar ratio of aluminum,
provided by the alumoxane, to transition metal, provided by the
metallocene, of the catalyst is between 20 and 200, and for
instance between 30 and 150, or preferably between 30 and 100.
[0140] The process of the invention is performed in at least one
continuous stirred tank reactor. As used herein, the term
"continuous stirred tank reactor", or "Continuously-Stirred Tank
Reactor" or "CSTR" is known in the art and refers to a tank having
a stirring means, wherein one or more reagents are continuously
introduced into the tank whilst at least one product stream is
continually removed from the tank.
[0141] A CSTR usually comprises a tank, and a stirring system to
mix reactants together. Feed and exit pipes are present to
introduce reactants and remove products. Reactants can be
continuously introduced into the reactor through ports at the top,
while products are continuously removed. The stirring system can
comprise stirring blades, which are also called agitators.
[0142] The present invention encompasses process of producing a
polyethylene. In an embodiment, the polyethylene may be produced in
at least one CSTR, for example at least two CSTRs connected in
series.
[0143] Preferably, the present invention encompasses a process for
preparing a polyethylene in at least one CSTR, under slurry
conditions. More preferably, the present invention encompasses a
process for preparing a polyethylene in at least two CSTR reactors
connected in series, under slurry conditions.
[0144] As used herein, the term "slurry" or "polymer slurry" or
"polymerization slurry" means substantially a multi-phase
composition including at least polymer solids and a liquid phase,
the liquid phase being the continuous phase. The solids include
catalyst and a polymerized olefin, such as polyethylene. The
liquids include an inert diluent, dissolved monomer such as
ethylene, optionally one or more co-monomers, optionally molecular
weight control agents, such as hydrogen; antistatic agents;
antifouling agents; scavengers; and other process additives.
[0145] As used herein, the term "diluent" refers to diluents in a
liquid state, liquid at room temperature and preferably liquid
under the pressure conditions in the CSTR. Diluents which are
suitable for being used in accordance with the present invention
may comprise but are not limited to hydrocarbon diluents such as
aliphatic, cycloaliphatic and aromatic hydrocarbon solvents, or
halogenated versions of such solvents. The preferred solvents are
C12 or lower, straight chain or branched chain, saturated
hydrocarbons, C5 to C9 saturated alicyclic or aromatic hydrocarbons
or C2 to C6 halogenated hydrocarbons. Non-limiting illustrative
examples of diluents are isohexane, hexane, butane, isobutane,
pentane, heptane, cyclopentane, cyclohexane, cycloheptane, methyl
cyclopentane, methyl cyclohexane, isooctane, benzene, toluene,
xylene, chloroform, chlorobenzenes, tetrachloroethylene,
dichloroethane and trichloroethane. In a preferred embodiment of
the present invention, said diluent is isohexane. However, it
should be clear from the present invention that other diluents may
as well be applied according to the present invention.
[0146] Suitable ethylene polymerization includes but is not limited
to homopolymerization of ethylene monomer, copolymerization of
ethylene and one or more higher 1-olefin co-monomers.
[0147] As used herein, the term "co-monomer" refers to olefin
co-monomers which are suitable for being polymerized with ethylene
monomers. Co-monomers may comprise but are not limited to aliphatic
C3-C20 alpha-olefins. Examples of suitable aliphatic C3-C20
alpha-olefins include propylene, 1-butene, 1-pentene,
4-methyl-1-pentene, 1-hexene, iso-hexene, 1-octene, 1-decene,
1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and
1-eicosene. The term "copolymer" refers to a polymer, which is made
by linking two different types of in the same polymer chain. The
term "homopolymer" refers to a polymer which is made by linking
ethylene monomers, in the absence of co-monomers. In an embodiment
of the present invention, said co-monomer is 1-butene.
[0148] In a preferred embodiment, suitable reactants for use in the
polymerization comprise the monomer ethylene, isohexane or hexane
as hydrocarbon diluent, a supported metallocene catalyst, and
optionally at least one co-monomer such as 1-butene.
[0149] The polymerization may be performed over a wide temperature
range. Preferably, the temperature is within the range of
65.degree. C. to 90.degree. C. A more preferred range is from
70.degree. C. to 85.degree. C., more preferably from 73.degree. C.
to 85.degree. C.
[0150] The reactor pressure is preferably held ranging from 0.65 to
10 bar.
[0151] In an embodiment of the present invention, the process may
further comprise a pre-polymerization step comprising contacting
ethylene with the metallocene catalyst. In an embodiment, said
pre-polymerization is performed in a reactor having a smaller size
compared to the polymerization reactor. Said pre-polymerization can
be performed in a loop reactor or a CSTR.
[0152] In an embodiment of the present invention, the polyethylene
has a monomodal molecular weight distribution.
[0153] In an embodiment of the present invention, the polyethylene
has a multimodal molecular weight distribution.
[0154] In a preferred embodiment of the present invention, the
polyethylene has a bimodal molecular weight distribution.
[0155] By the term "monomodal polyethylene" or "polyethylene with a
monomodal molecular weight distribution" it is meant, polyethylene
having one maxima in their molecular weight distribution curve
defined also as unimodal distribution curve. By the term
"polyethylene with a bimodal molecular weight distribution" or
"bimodal polyethylene" it is meant, polyethylene having a
distribution curve being the sum of two unimodal molecular weight
distribution curves. By the term "polyethylene with a multimodal
molecular weight distribution" or "multimodal polyethylene product"
it is meant polyethylene with a distribution curve being the sum of
at least two, preferably more than two unimodal distribution
curves.
[0156] The process according to the present invention may be
performed in the presence of at least one antifouling agent.
[0157] As used in the present invention, the term "antifouling
agent" refers to material that prevents fouling of the inside of
the reactor wall.
[0158] In an embodiment, the antifouling agent comprises cationic
agents, anionic agents, nonionic agents, organometallic agents,
polymeric agents or mixtures thereof.
[0159] Suitable examples of cationic agents can be selected from
quaternary ammonium, sulfonium or phosphonium salts with long,
preferably C.sub.5-20, hydrocarbon chain, for example chloride,
sulfate, nitrate, or hydrogen phosphate salts thereof.
[0160] Examples of suitable anionic agents can be selected from
sulfated oils, sulfated amide oils, sulfated ester oils, fatty
alcohol sulfuric ester salts, alkyl sulfuric ester salts, fatty
acid ethyl sulfonic acid salts, alkyl sulfonic acid salts, for
example sodium alkyl sulfonates, alkylnaphthalene-sulfonic acid
salts, alkylbenzene-sulfonic acid salts, phosphoric esters, for
example alkyl phosphonates, alkyl phosphates, alkyl dithiocarbamate
or mixtures thereof.
[0161] Examples of suitable nonionic agents can be selected from
partial fatty acid esters of polyhydric alcohols; alkoxylated fatty
alcohols such as ethoxylated or propoxylated fatty alcohols;
polyethylene glycol (PEG) esters of fatty acids and alkylphenols;
glyceryl esters of fatty acids and sorbitol esters; ethylene oxide
adducts of fatty amines or fatty acid amides; ethylene oxide
adducts of alkylphenols; ethylene oxide adducts of alkylnaphthols;
polyethylene glycol, and fatty acid esters of alkyldiethanolamines,
or mixtures thereof.
[0162] Examples of suitable organometallic agents can be selected
from neoalkyl titanates and zirconates, or mixtures thereof.
[0163] Examples of suitable polymeric agents can be selected from
polyoxyalkylenic compounds such as polyethylene glycol hexadecyl
ether; ethylene oxide/propylene oxide copolymers; or mixtures
thereof. For example, suitable ethylene oxide/propylene oxide
copolymer antifouling agent can comprise one or more
--(CH.sub.2--CH.sub.2--O).sub.k-- where each k is in the range from
1 to 50; and one or more --(CH.sub.2--CH(R)--O).sub.n-- wherein R
comprises an alkyl group having from 1 to 6 carbon atoms and each n
is in the range from 1 to 50, and terminated by a R' and a R'' end
groups, wherein R' is OH or an alkoxy having from 1 to 6 carbon
atoms and R'' is H or an alkyl having from 1 to 6 carbon atoms. In
an embodiment, the antifouling agent is a block polymer, more
preferably a tri-block polymer. In an embodiment, the antifouling
agent is a block polymer of general formula:
R'--(CH.sub.2--CH.sub.2--O).sub.k--(CH.sub.2--CH(R)--O).sub.n--(CH.sub.2-
--CH.sub.2--O)m-R'' (VII) or
R'--(CH.sub.2--CH(R)--O).sub.n--(CH.sub.2--CH.sub.2--O).sub.b--(CH.sub.2-
--CH(R)--O).sub.c--R'' (VIII),
[0164] wherein R comprises an alkyl group; R' and R'' are end
groups; k is from 1 to 50; n is from 1 to 50; m is greater than or
equal to 1; a is from 1 to 50; b is from 1 to 50; and c is from 0
to 50; k and m and a and c may be the same or different. Preferably
R is a C1 to C3 alkyl group. More preferably, R is a methyl group.
Preferably, in one embodiment, k is greater than 1 and m is greater
than 1. Also preferably, in another embodiment a is 0 or c is 0.
Preferred R' and R'' groups include H, OH, alkyl, and alkoxy
groups. Preferred alkyl groups are C1 to C3 alkyl groups. Preferred
alkoxy groups are C1 to C3 alkoxy groups. In formulae (VII) and
(VIII) above, it is preferred that R' is OH or an alkoxy group,
preferably OH or a C1 to C3 alkoxy group. Further, it is preferred
that R'' is H or an alkyl group, preferably H or a C1 to C3 alkyl
group. A particularly preferred polymer has general formula (IX):
R'--(CH.sub.2--CH.sub.2--O).sub.k--(CH.sub.2--CH(CH.sub.3)--O).sub.n--(CH-
.sub.2--CH.sub.2--O).sub.m--R'' (IX), wherein R', R'', k, n, and m
independently are as defined anywhere above. A further preferred
polymer has general formula (X):
OH--(CH.sub.2--CH.sub.2--O).sub.k--(CH.sub.2--CH(R)--O).sub.n--(CH.sub.2--
-CH.sub.2--O).sub.m--H (X), wherein R, k, n, and m independently
are as defined anywhere above. It will be appreciated that, by
virtue of the preferred molecular weights for the antifouling agent
and the preferred ethylene oxide contents in the present
antifouling agent given above, preferred values for a, b, c, k, n,
and m can be derived. Preferably, the weight percentage of ethylene
oxide in the antifouling agent is in the range of from 5 to 40%,
more preferably from 8 to 30%, even more preferably from 10 to 20%,
most preferably about 10%. In an embodiment, the ethylene
oxide/propylene oxide copolymer has a molecular weight (MW) greater
than 1000 Daltons, preferably greater than 2000 Daltons, more
preferably in the range from 2000-4500 Daltons.
[0165] Examples of suitable commercially available antifouling
agents include those under the trade designation Armostat.RTM.
(such as Armostate 300
(N,N-bis-(2-hydroxyethyl)-(C.sub.10-C.sub.20)alkylamine), Armostate
410 (bis(2-hydroxyethyl)cocoamine), and Armostat.RTM. 600
(N,N-bis(2-hydroxy-ethyl)alkylamine) from Akzo Nobel Corporation;
those under the trade designation Chemax X997.RTM. (>50% of
dicocoalkyl-dimethyl ammonium chloride, about 35% 1-hexene, <2%
isopropanol, and <1% hexane); those under the trade designation
Atmere 163 (N,N-Bis(2-hydroxy-ethyl) alkylamine) from ICI Americas;
those under the trade designation Statsafe 6000
(dodecylbenzenesulfonic acid) from Innospec Limited; those under
the trade designation Octastat.RTM. 3000 (about 40-50% toluene,
about 0-5% propan-2-ol, about 5-15% DINNSA (dinonyinaphthasulphonic
acid), about 15-30% solvent naphtha, about 1-10% trade secret
polymer containing N, and about 10-20% trade secret polymer
containing S) from Octel Performance Chemicals; those under the
trade designation Kerostate 8190 (about 10-20% alkenes (polymer
with sulfur dioxide), about 3-8% benzenesulfonic acid
(4-C10-13-sec-alkyl derivatives) and organic solvent) from BASF,
those under the trade designation Stadis.RTM. 450 (about 14 wt % of
polybutene sulfate, about 3 wt % of aminoethanolepichlorohydrin
polymer, about 13 wt % of alkylbenzenesulfonic acid, about 70 wt %
of toluene and trace amounts of quaternary ammonium salt of
aliphatic alkyl and propyl alcohol) from E. I. Du Pont de Nemours
& Co.; Synperonic PEL121
(ethyleneoxide-propyleneoxide-ethyleneoxide block copolymer, about
10% of propyleneoxide, MW about 4400 Da) from Uniqema, pluronic
31R1 from BASF, and the like. Preferred examples of antifouling
agents are dodecylbenzenesulfonic acid or
ethyleneoxide-propyleneoxide block copolymer.
[0166] Preferred examples of antifouling agents for use in the
invention are Synperonic PEL121, Statsafe 6000, Pluronic 31R1,
Stadis 450, Chemax X997.RTM..
[0167] Preferably, antifouling agent is fed to the reactor as a
composition with a solvent, preferably dissolved in a solvent.
Preferably, the solvent is selected from C4-C10 aliphatic and
olefin compounds. Preferably, the solvent is selected from
unsaturated (olefin) C4-C10 compounds. In an embodiment, said
solvent is selected from hexane, isohexane, hexene, cyclohexane, or
heptane.
[0168] Preferably, antifouling agent is used in the reactor at a
level of from 0.1 to 50 ppm as a function of the diluent in the
polymer slurry, preferably from 1.0 to 20 ppm, preferably from 1.0
to 10.0 ppm, preferably from 2.0 to 6.0 ppm.
[0169] The process according to the invention has the advantage of
preparing bimodal polyethylene fluff having low average particle
size.
[0170] A process producing polyethylene having low particle size
allows better and easier removal of the diluent used in the
polymerization. The small size of the fluff particles allow better
solids and level control on the reactor, thereby preventing or
reducing settling issues. Furthermore, plugging of transfer and
discharges lines can be minimized and even avoided.
[0171] In one embodiment of the present invention, the polyethylene
is particulate and has a D50 ranging from 100 to 400 .mu.m, with
D50 being defined as the particle size for which fifty percent by
weight of the particles has a size lower than the D50. In an
embodiment, the polyethylene has a D50 of at most 350 .mu.m,
preferably at most 300 .mu.m, preferably at most 250 .mu.m.
[0172] The measurement of the particle size of the polyethylene can
be made by sieving techniques. The sieving can be performed with a
set of calibrated sieves according to ASTM D-1921-89 particle size
(sieve analysis) of Plastic Materials, Method A. Alternatively, the
particle size may be measured by using optical measurements,
preferably with a Camsizer.
[0173] In one embodiment of the present invention, the
"polyethylene" or "polyethylene resin" is in the form of a fluff or
a powder. For the purpose of this invention, "resin", "powder" or
"fluff" is defined as the polymer material after it exits the
polymerization reactor (or final polymerization reactor in the case
of multiple reactors connected in series).
[0174] The polyethylene preferably has a Si content of at most 60
ppm by weight, preferably from 5 to 60 ppm by weight. The Si
content is measured by x-ray fluorescence (XRF).
[0175] In some preferred embodiment, the atomic Si content of the
polyethylene is from 5 to 60 ppm by weight, preferably from 5 to 55
ppm, more preferably from 5 to 50 ppm. Si content is measured by
x-ray fluorescence (XRF) according to following procedure:
[0176] 1. Preparing the 1 mm thick sample discs of polyethylene for
measuring Si content by XRF:
[0177] 15 g of the polyethylene are placed between 2 sheets of
Melimex 401 of 125.mu., which is then placed between two metallic
plates and pressed together under heating to 200.degree. C. An
increasing pressure up to 4 bar is then exerted for 2 minutes in
the Carver 2518.RTM. press. The sample is cooled until hardened,
upon which the Melimex sheets are removed. The sample is rolled on
itself. The rolled sample is again placed between the Melimex
sheets and heated and pressed as before. The sample is then
re-rolled on itself again and the heating and pressure applied once
more, except that a mould of about 1 mm is included in the inside
support of the metallic plate. An increasing pressure up to 4 bar
is applied for 10 minutes. The sample is cooled, released from the
mould and then punched to obtain 3 discs of 50 mm in diameter and 1
mm in thickness.
[0178] 2. Measuring the Si content
[0179] XRF is measured on a Philips PW 2400 equipped with an RX
tube and a chrome anode using the PANanalytical softwares
"SuperQ--software for xray analyzers" version 3.0 and "X40".
[0180] A standard reference is used in this method in the form of
Si-doped pearls (prepared from aqueous solution of 1000 ppm by
weight Si) to cover the equivalent range of Si-content of the
polyethylene sample to be measured anywhere from 0 to 1050 ppm. The
amount of Si on these pearls is determined by their fluorescence
intensity using application 22 of the "X40" software.
[0181] The sample holders with the sample polyethylene are held
under vacuum. The internal surface of the sample holder is bare; No
retention film is used. Using the "SuperQ" software, each Si
measurement is made twice and on both surfaces of the sample disc.
Thus, 4 measurements are made on each sample disc. Results are
expressed in ppm.
[0182] Note that the measurements, such as D50 and XRF are made on
the polyethylene obtained from the reactor (the fluff), prior to
additivation, extrusion and pelletizing.
[0183] The present invention also encompasses polyethylene produced
according to the present process. The polyethylene of the present
invention is suitable for a wide variety of applications.
[0184] The present invention also encompasses polyethylene prepared
in at least one CSTR in the presence of at least one supported
metallocene catalyst, wherein said polyethylene has a D50 ranging
from 100 to 400 .mu.m, with D50 being defined as the particle size
for which fifty percent by weight of the particles has a size lower
than the D50. Preferably, the polyethylene has a D50 of at most 350
.mu.m, preferably at most 300 .mu.m, preferably at most 250
.mu.m.
[0185] The present invention also encompasses polyethylene prepared
in at least one CSTR in the presence of at least one supported
metallocene catalyst, wherein said polyethylene has a Si content of
at most 60 ppm by weight, for example at most 55 ppm by weight, for
example at most 50 ppm by weight, preferably from 5 to 60 ppm by
weight, for example from 5 to 55 ppm by weight, for example from 5
to 50 ppm by weight.
[0186] The present invention also encompasses polyethylene prepared
in at least one CSTR in the presence of at least one supported
metallocene catalyst, wherein said polyethylene has a D50 ranging
from 100 to 400 .mu.m, and a Si content of at most 60 ppm by
weight, with D50 being defined as the particle size for which fifty
percent by weight of the particles has a size lower than the D50.
Preferably, the polyethylene has a D50 of at most 350 .mu.m,
preferably at most 300 .mu.m, preferably at most 250 .mu.m, and a
Si content of for example at most 55 ppm by weight, for example at
most 50 ppm by weight, preferably from 5 to 60 ppm by weight, for
example from 5 to 55 ppm by weight, for example from 5 to 50 ppm by
weight.
[0187] One embodiment encompasses a polyethylene prepared according
to the process according to the present invention, wherein the
polyethylene has a bimodal molecular weight distribution.
[0188] One embodiment encompasses a polyethylene comprising a
polyethylene prepared according to the process according to the
present invention, wherein the polyethylene has a bimodal molecular
weight distribution and was prepared in the presence of 1-butene as
co-monomer.
[0189] Another embodiment encompasses a polyethylene prepared
according to the process according to the present invention,
wherein the polyethylene has a monomodal molecular weight
distribution.
[0190] The present inventors have found that polyethylene produced
according to the present process have an improved homogeneity. The
process provides advantages such as ease of processing.
[0191] The present invention also encompasses formed articles
comprising the polyethylene produced according to the present
process. Due to the improved mechanical properties of the
polyethylene of the present invention, it is suitable for a wide
variety of applications. Preferred articles are films, pipes,
preferably pipes PE-RT (polyethylene of raised temperature
resistance), injection molded articles, injection stretch blow
molded articles, rotomoulded articles, caps and closures, fibers,
sheets, containers, and foams. Polyethylene of raised temperature
resistance (PERT), as defined in ISO-1043-1, is a class of
polyethylene materials for high temperature applications, such as
high temperature pipe applications. By the term "polyethylene of
raised temperature resistance" (PERT) is meant polyethylene which
is resistant to temperature according to standard EN-ISO 22391 and
does not require additives to meet its function of resistance to
dilatation.
[0192] In another embodiment, the invention provides an article
comprising a polyethylene preferably prepared in at least one
continuously stirred tank reactor, using a process comprising the
step of: polymerizing ethylene in the presence of at least one
supported metallocene catalyst, a diluent, optionally one or more
co-monomers, and optionally hydrogen, thereby obtaining the
polyethylene, wherein the support of said supported metallocene
catalyst has a D50 value within the range of from 3 .mu.m to 25
.mu.m, with D50 being defined as the particle size for which fifty
percent by weight of the particles has a size lower than the D50;
and D50 being measured by laser diffraction analysis on a Malvern
type analyzer, and wherein the support of said supported
metallocene catalyst has a surface area within the range of from
100 to 500 m.sup.2/g.
[0193] The following non-limiting example illustrates the
invention.
EXAMPLES
[0194] Silica Supports Used in the Following Examples are Listed in
Table 1:
TABLE-US-00001 TABLE 1 Silica PD-10001 PD-10001-Ti H121C ES70W SA
(m.sup.2/g) 285 262 790 268 PV (mL/g) 1.57 1.54 0.8 1.52 D50
(.mu.m) 12.5 12.5 15 43 Span 0.98 0.98 1.16 1.62 Commercial PQ
PD-10001 from PQ Asahi Glass PQ source Corporation Corporation
Company, Corpo- Titanated as Limited ration described for INV-2
Abbreviations: SA: surface area; PV: pore volume
[0195] Supported Metallocene Catalyst System:
[0196] Supported Catalyst INVENTIVE 1 (INV-1)
[0197] 1. MAO Treatment
[0198] 20 g of dried silica PD-10001 were introduced in a 500 mL
round-bottomed flask. Toluene was added and the suspension was
stirred at 100 rpm. MAO (30 wt % in toluene) was added dropwise via
a dropping funnel and the resulting suspension was heated at
110.degree. C. (reflux) for 4 hours. The amount of added MAO was
calculated to reach the desired Al loading. After the reflux, the
suspension was cooled down to room temperature and the mixture was
filtered through a glass frit. The recovered powder was washed with
toluene and pentane before being dried under reduced pressure
overnight, leading to SMAO free-flowing powder.
[0199] 2. Metallocene Treatment
[0200] In a 250 mL round bottom flask, 9.8 g of the above-obtained
SMAO silica were suspended in 80 mL of toluene. Then, 0.2 g of
ethylene-bis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride in
a suspension of 20 mL of toluene were added to the suspended
silica-containing support. The resulting suspension was stirred at
100 rpm for 2 hours at room temperature. Finally, the obtained
catalyst was filtered, washed with toluene and pentane before being
dried overnight, leading to catalyst INV-1.
[0201] Supported Catalyst INVENTIVE 2 (INV-2)
[0202] 1. Support Modification
[0203] In a 250 mL round bottom flask conditioned under a light
nitrogen flow, 25 g of silica PD-10001 were stirred at 60 rpm and
dried at 110.degree. C. overnight. 190 mL of dry hexane were then
added. The suspension was cooled at 0.degree. C. and 3.2 mL of
VertecBip (20:80 weight ratio of Ti(OC.sub.4H.sub.9).sub.4 to
Ti(OC.sub.3H.sub.7).sub.4) were added dropwise to impregnate the
support. The suspension was mixed for 20 hours at 0.degree. C. The
solvent was removed under reduced pressure and the resulting silica
was dried under a nitrogen flow at 450.degree. C. for 4 hours. The
Ti-impregnated silica had a Ti content of 2 wt %.
[0204] 2. MAO Treatment
[0205] 20 g of modified-silica were introduced in a 500 mL
round-bottomed flask. Toluene was added and the suspension was
stirred at 100 rpm. MAO (30 wt % in toluene) was added dropwise via
a dropping funnel and the resulting suspension was heated at
110.degree. C. (reflux) for 4 hours. The amount of added MAO was
calculated to reach the desired Al loading. After the reflux, the
suspension was cooled down to room temperature and the mixture was
filtered through a glass frit. The recovered powder was washed with
toluene and pentane before being dried under reduced pressure
overnight.
[0206] 3. Metallocene Treatment
[0207] In a 250 mL round bottom flask, 9.8 g of the above-obtained
SMAO silica were suspended in 80 mL of toluene. Then, 0.2 g of
ethylene-bis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride in
a suspension of 20 mL of toluene were added to the suspended
silica-containing support. The resulting suspension was stirred at
100 rpm for 2 hours at room temperature. Finally, the obtained
catalyst was filtered, washed with toluene and pentane before being
dried overnight, leading to catalyst INV-2.
[0208] Supported Catalyst COMPARATIVE 1 (COMP-1)
[0209] 1. MAO Treatment
[0210] 20 g of dried silica H121C were introduced in a 500 mL
round-bottomed flask. Toluene was added and the suspension was
stirred at 100 rpm. MAO (30 wt % in toluene) was added dropwise via
a dropping funnel and the resulting suspension was heated at
110.degree. C. (reflux) for 4 hours. The amount of added MAO was
calculated to reach the desired Al loading. After the reflux, the
suspension was cooled down to room temperature and the mixture was
filtered through a glass frit. The recovered powder was washed with
toluene and pentane before being dried under reduced pressure
overnight, leading to SMAO free-flowing powder.
[0211] 2. Metallocene Treatment
[0212] In a 250 mL round bottom flask, 9.8 g of the above-obtained
SMAO silica were suspended in 80 mL of toluene. Then, 0.2 g of
ethylene-bis(4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride in
a suspension of 20 mL of toluene were added to the suspended
silica-containing support. The resulting suspension was stirred at
100 rpm for 2 hours at room temperature. Finally, the obtained
catalyst was filtered, washed with toluene and pentane before being
dried overnight, leading to catalyst COMP-1.
[0213] Supported Catalyst COMPARATIVE 2 (COMP-2)
[0214] Catalyst COMP-2 was produced with the same recipe as COMP-1
using ES70W silica.
[0215] 1-Process for Preparing Polyethylene Having a Monomodal
Molecular Weight Distribution
[0216] Monomodal polyethylene resins were prepared in one CSTR. The
reaction conditions are given in table 2 as well as the properties
of the polyethylene.
TABLE-US-00002 TABLE 2 Polymerization conditions Monomodal CSTR
grades Catalyst name COMP-1 COMP-2 Inv-1 Inv-2 Throughput kg 5.1
5.2 5.2 5.2 PE/hour Tibal (ppm) 35 39 42 33 Antifouling 4 4.1 4.3
3.5 (Synperonic) (ppm) Mileage (g:g) 3100 5580 6293 11201 Si
content (ppm 99 56 49 27.5 by weight) measured by XRF Ethylene
(kg/hour) 6 6 6 6 H2/C2 molar ratio 0.0015 0.0012 0.00013 0.0015
Hexane (kg/hour) 55.5 55.5 55.2 55.3 Temperature (.degree. C.) 83
83 83 83 Residence Time 1.27 1.27 1.28 1.27 (hours) MI-2 (g/10 min)
4.8 3.1 4.5 4.2 Density (g/cm.sup.3) 0.961 0.96 0.961 0.961 D50
(.mu.m) 622 549 222 212 Bulk Density 0.41 0.41 0.44 0.42
(g/cm.sup.3)
[0217] Density was measured according to ASTM D-1505 at 23.degree.
C. MI-2 was determined according to ISO 1133:1997, condition D, at
190.degree. C. and under a load of 2.16 kg. The D50 of the
polyethylene particles was determined by sieving technique
according to ASTM D 1921-89 particle size (sieve analysis) of
Plastic Materials, Method A.
[0218] The process according to the invention allowed preparing
monomodal polyethylene fluff having low average particle size,
compared to the comparative process. Also, the polyethylene
according to the invention has reduced catalytic residues. The
catalysts according to the invention showed increased activity
compared to the comparative example, and the activity was even at
least twice as high for the titanated catalyst. The polyethylene
with low particle size allowed better and easier removal of the
diluent used in the polymerization (here: hexane). The small
particle size also allowed better solids and level control on the
reactor, thereby preventing or reducing settling issues.
Furthermore, plugging of transfer and discharges lines was
minimized and even avoided.
[0219] Process for Preparing Polyethylene Having a Bimodal
Molecular Weight Distribution
[0220] Polyethylene resins with bimodal molecular weight
distribution were prepared in two CSTRs connected in series. These
polyethylenes were suitable for preparing films. The reaction
conditions are given in table 3 as well as the properties of the
polyethylene.
TABLE-US-00003 TABLE 3 Polymerization conditions Bimodal RUN 1 RUN
2 Reactor 1 Reactor 2 Reactor 1 Reactor 2 Catalyst COMP-1 Inv-2
Throughput kg 2.5 4.1 2.6 4.3 PE/hour Tibal (ppm) 40 39 40 39
Antifouling 3.8 3.6 3.1 2.5 (Synperonic) (ppm) Mileage (g:g) 4056
6650 14471 22078 Ethylene (kg/hour) 4.1 1.42 4.2 1.45 Si content
(ppm 76 47 22 -- by weight) measured by XRF H2/C2 molar ratio
0.0039 0 0.0037 0 1 butene (g/hour) 0 76 0 85 Hexane (kg/hour) 38
5.5 36 5.3 Temperature (.degree. C.) 83 75 83 75 Residence Time
1.19 1.05 1.23 0.96 (hours) MI-2 (g/10 min) 14 1.03 16 0.92 Density
(g/cm.sup.3) 0.966 0.951 0.967 0.950 d50 (.mu.m) 632 862 219 225 BD
(g/cm.sup.3) 0.42 0.41 0.41 0.39
[0221] Density was measured according to ASTM D-1505 at 23.degree.
C. MI-2 was determined according to ISO 1133:1997, condition D, at
190.degree. C. and under a load of 2.16 kg. The D50 of the
polyethylene particles was determined by sieving technique
according to ASTM D 1921-89 particle size (sieve analysis) of
Plastic Materials, Method A.
[0222] The process according to the invention allowed preparing
bimodal polyethylene fluff having low average particle size,
compared to the comparative process. Also, the polyethylene
according to the invention has reduced catalytic residues. The
catalyst according to the invention had a drastically higher
activity compared to the comparative catalyst, and still allowed
preparing small size polyethylene powder. The polyethylene with low
particle size allowed better and easier removal of the diluent used
in the polymerization (here: hexane). The small particle size also
allowed better solids and level control on the reactor, thereby
preventing or reducing settling issues. Furthermore, plugging of
transfer and discharges lines was minimized and even avoided.
Furthermore, the bimodal polyethylene produced by the process
according to the invention displayed better homogeneity (less
gels).
* * * * *