U.S. patent application number 15/231808 was filed with the patent office on 2016-12-01 for solid component of catalyst for the (co) polymerization of ethyleneand process for its use.
This patent application is currently assigned to VERSALIS S.p.A.. The applicant listed for this patent is VERSALIS S.p.A.. Invention is credited to Corrado ADESSO, Giuseppe CONTI, Francesco MASI, Francesco MENCONI.
Application Number | 20160347892 15/231808 |
Document ID | / |
Family ID | 34593786 |
Filed Date | 2016-12-01 |
United States Patent
Application |
20160347892 |
Kind Code |
A1 |
CONTI; Giuseppe ; et
al. |
December 1, 2016 |
SOLID COMPONENT OF CATALYST FOR THE (CO) POLYMERIZATION OF
ETHYLENEAND PROCESS FOR ITS USE
Abstract
Catalyst and solid component of catalyst for the
(co)polymerization of ethylene, comprising titanium, magnesium,
chlorine, a protic organo-oxygenated compound D.sub.p and a neutral
aprotic electron-donor compound D, in the following molar ranges:
Mg/Ti=1.0-50; D/Ti=1.0-15; Cl/Ti=6.0-100; Dp/D=0.05-3; and a
process for obtaining said component.
Inventors: |
CONTI; Giuseppe; (Milano,
IT) ; ADESSO; Corrado; (Brindisi, IT) ;
MENCONI; Francesco; (San Donato Milanese-Milano, IT)
; MASI; Francesco; (Sant'Angelo Lodigiano-Lodi,
IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VERSALIS S.p.A. |
San Donato Milanese (Milano) |
|
IT |
|
|
Assignee: |
VERSALIS S.p.A.
San Donato Milanese (Milano)
IT
|
Family ID: |
34593786 |
Appl. No.: |
15/231808 |
Filed: |
August 9, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13649248 |
Oct 11, 2012 |
9447207 |
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15231808 |
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10578873 |
Dec 15, 2006 |
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PCT/EP2004/012746 |
Nov 9, 2004 |
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13649248 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08F 210/16 20130101;
C08F 10/02 20130101; C08F 10/02 20130101; C08F 10/02 20130101; C08F
210/16 20130101; C08F 2500/19 20130101; C08F 2500/12 20130101; C08F
4/6543 20130101; C08F 4/651 20130101; C08F 2500/24 20130101; C08F
2500/18 20130101; C08F 210/14 20130101 |
International
Class: |
C08F 210/16 20060101
C08F210/16 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 14, 2003 |
IT |
MI2003A002206 |
Sep 10, 2004 |
IT |
MI2004A001722 |
Claims
1. A solid component of catalyst for a (co)polymerization of
ethylene, comprising titanium, magnesium, chlorine, an
organo-oxygenated protic compound D.sub.p, and a neutral
electron-donor aprotic compound D, in the following molar ratio
ranges: Mg/Ti=1.0-50; D/Ti=1.0-15; Cl/Ti=6.0-100;
D.sub.p/D=0.05-3.
2. The solid component according to claim 1, additionally
comprising an inert granular solid, in a quantity ranging from 10
to 90% by weight with respect to the total weight of the solid
component.
3. The solid component according to claim 2, wherein said inert
granular solid is in a quantity ranging from 25 to 50% by
weight.
4. The solid component according to claim 2, wherein said inert
granular solid is selected from the group consisting of: silica,
titania, silico-aluminates, calcium carbonate, and magnesium
chloride, and having average dimensions of the inert granule solid
ranging from 10 .mu.m to 300 .mu.m.
5. The solid component according to claim 4, wherein said inert
granular solid consists of microspheroidal silica having an average
diameter ranging from 20 to 100 .mu.m, a BET surface area ranging
from 150 to 400 m.sup.2/g, a total porosity equal or higher than
80% and an average pore radius of 50 to 200 .ANG..
6. The solid component according to claim 1, wherein the molar
ratio ranges are: Mg/Ti=1.5-10; D/Ti=3.0-8.0; Cl/Ti=10-25;
D.sub.p/D=0.1-2.0.
7. The solid component according to claim 1, wherein said ratio
D.sub.p/D ranges from 0.2 to 1.0.
8. The solid component according to claim 1, wherein said
organo-oxygenated protic compound D.sub.p is selected from
compounds having the following formula (II): R-(A).sub.m-OH (II)
wherein: R is an aliphatic, cyclo-aliphatic or aromatic radical,
optionally fluorinated, containing from 1 to 30 carbon atoms; A is
one of divalent groups having the formula CR.sup.1R.sup.2, CO, SCO
and SO, wherein each R.sup.1 and R.sup.2 is independently hydrogen
or an aliphatic or aromatic group having from 1 to 10 carbon atoms;
and m is 0 or 1.
9. The solid component according to claim 1, wherein said
organo-oxygenated protic compound D.sub.p is selected from the
group consisting of aliphatic or aromatic alcohols and organic
acids, having from 2 to 10 carbon atoms.
10. The solid component according to claim 1, wherein said aprotic
electron-donor compound D is a coordinating organic compound having
from 3 to 20 carbon atoms, comprising at least one heteroatom of
non-metallic compounds of groups 15 and 16.
11. The solid component according to claim 1, wherein said
electron-donor compound D is at least one selected from the group
consisting of ketones, ethers, esters, amines, amides, thioethers,
and xanthates, linear or cyclic, and aliphatic or aromatic, having
from 4 to 10 carbon atoms.
12. The solid component according to claim 10, wherein said
compound D is selected from the group consisting of dibutyl ether,
dihexyl ether, methylethyl ketone, diisobutyl ketone,
tetrahydrofuran, dioxane, ethyl acetate, butyrolactone.
13. The solid component according to claim 1, wherein said titanium
is present in a quantity ranging from 1 to 10% by weight.
14. A process for the preparation of a solid component comprising
titanium, magnesium, chlorine, an organo-oxygenated protic compound
D.sub.p, and a neutral electron-donor aprotic compound D, in the
following molar ratio ranges: Mg/Ti=1.0-50; D/Ti=1.0-15;
Cl/Ti=6.0-100; D.sub.p/D=0.05-3, comprising reacting, in an inert
liquid medium, a solid precursor containing titanium, magnesium,
chlorine, an aprotic electron-donor compound D and optionally an
inert granular solid in the following molar ratios: Mg/Ti=1-50;
D/Ti=2.0-20; Cl/Ti=6-100 with protic organo-oxygenated compound
D.sub.p, in such a quantity that the molar ratio D.sub.p/D ranges
from 0.1 to 1.2, until equilibrium is reached, wherein said inert
granular solid is in a quantity ranging from 0 to 95%.
15. The process according to claim 14, wherein said molar ratios
are: Mg/Ti=1.5-10; D/Ti=4.0-12; Cl/Ti=10-30, and wherein said inert
granular solid is in a quantity ranging from 20 to 60% by weight
with respect to the total weight of the precursor.
16. The process according to claim 14, wherein the molar ratio
D.sub.p/D ranges from 0.2 to 1.2.
17. The process according to claim 14, wherein said reaction is
carried out at a temperature ranging from 40 to 100.degree. C., for
a period varying from 5 minutes to 5 hours.
18. The process according to claim 17, wherein said reaction is
carried out at a temperature ranging from 60 to 80.degree. C., for
a period of 5 to 60 minutes.
19. A catalyst for the (co)polymerization of ethylene, where the
catalyst is obtained by a process comprising reacting said solid
component according to claim 1 with a co-catalyst comprising a
hydrocarbyl compound of a metal selected from the group consisting
of Al, Ga, Mg, Zn and Li.
20. The catalyst according to claim 19, wherein the atomic ratio
between the metal in the co-catalyst and titanium in the solid
component of catalyst ranges from 10:1 to 500:1.
21. The catalyst according to claim 19, comprising titanium,
magnesium, aluminum and chlorine, wherein said co-catalyst
comprises an alkylic organometallic compound of aluminum.
22. The catalyst according to claim 21, wherein said organometallic
compound of aluminum is at least one aluminum tri-alkyl comprising
from 1 to 10 carbon atoms in each alkyl group.
23. The catalyst according to claim 19, wherein the solid component
and the co-catalyst are contacted in situ in a polymerization
reactor.
24. The catalyst according to claim 19, wherein said solid
component is activated before contact with said co-catalyst, by
reaction with an aluminum alkyl or alkyl chloride represented by
formula (III): AlR'.sub.nX.sub.(3-n) (III) wherein: R' is a linear
or branched alkyl radical containing from 1 to 20 carbon atoms; X
is H or Cl; and n is a decimal number having a value ranging from 1
to 3; wherein an Al/(D+D.sub.p) ratio between the aluminium moles
in said compound having formula (III) and the total of D and
D.sub.p moles in said solid component ranges from 0.1 to 1.5.
25. The catalyst according to claim 24, wherein said R' in formula
(III) is a linear or branched aliphatic radical, having from 2 to 8
carbon atoms.
26. The catalyst according to claim 24, wherein said Al/(D+D.sub.p)
ratio ranges from 0.2 to 1.3.
27. The catalyst according to 24, wherein said solid component is
activated by a first reaction with an aluminum trialkyl (n=3 in
formula (III)), and successively in a second reaction with an
aluminum dialkyl chloride (n=2, X=Cl, in formula (III)), in such a
quantity that the overall molar ratio Al/(D+D.sub.p) ranges from
0.1 to 1.3.
28. The catalyst according to claim 27, wherein, in said first
reaction, the molar ratio AlR.sub.3/(D+D.sub.p) ranges from 0.1 to
0.4 and, in the second reaction, the molar ratio
AlR.sub.2Cl/(D+D.sub.p) ranges from 0.2 to 0.6.
29. A process for the (co)polymerization of ethylene, comprising
reacting ethylene and optionally at least one alpha-olefin, under
suitable polymerization conditions, in the presence of said
catalyst according to claim 19.
30. The process according to claim 29, comprising carrying out a
fluid-bed method, wherein a gaseous stream of ethylene and optional
alpha-olefin is reacted in the presence of a quantity of catalyst,
at a temperature ranging from 70 to 115.degree. C., and at a
pressure ranging from 500 to 1000 kPa.
31. The process according to claim 30, wherein said gaseous stream
is introduced from the bottom of the polymerization reactor,
partially comprising a stream in liquid form.
32. The process according to claim 30, in the presence of a
catalyst for the (co)polymerization of ethylene, which is obtained
by means of contact and reaction of a solid component of catalyst
for a (co)polymerization of ethylene, comprising titanium,
magnesium, chlorine, an organo-oxygenated protic compound D.sub.p,
and a neutral electron-donor aprotic compound D, in the following
molar ratio ranges: Mg/Ti=1.0-50; D/Ti=1.0-15; Cl/Ti=6.0-100;
D.sub.p/D=0.05-3, with a co-catalyst comprising a hydrocarbyl
compound of a metal selected from Al, Ga, Mg, Zn and Li, wherein
said solid component is activated before contact with said
co-catalyst, by reaction with an aluminum alkyl or alkyl chloride
represented by formula (III): AlR'.sub.nX.sub.(3-n) (III) wherein:
R' is a linear or branched alkyl radical containing from 1 to 20
carbon atoms; X is H or Cl; and n is a decimal number having a
value ranging from 1 to 3; wherein an Al/(D+D.sub.p) ratio between
the aluminium moles in said compound having formula (III) and the
total of D and D.sub.p moles in said solid component ranges from
0.1 to 1.5.
33. The process according to claim 29, wherein the molar ratio with
ethylene ranges from 0.1 to 1.0.
34. The process according to claim 29, wherein said .alpha.-olefin
is selected from the group consisting of 1-butene, 1-hexene and
1-octene and is in a quantity that the molar ratio with ethylene
ranges from 0.1 to 0.4.
35. The process according to claim 29, comprising obtaining linear
polyethylene having a density ranging from 0.915 to 0.950 g/ml.
36. The process according to claim 30, comprising obtaining linear
polyethylene having a density lower than 0.915 g/ml, and
co-polymerizing, in gas phase, a gaseous mixture comprising
ethylene and at least one alpha-olefin having from 4 to 10 carbon
atoms.
37. The process according to claim 36, wherein the gaseous mixture
of ethylene and the at least one alpha-olefin is reacted in the
presence of a quantity of catalyst, at a temperature ranging from
70 to 95.degree. C., and a pressure ranging from 500 to 1000
kPa.
38. The process according to claim 36, wherein said alphaolefin is
selected from the group consisting of 1-butene, 1-hexene and
1-octene, and is in a quantity that the molar ratio with respect to
ethylene ranges from 0.1 to 0.4.
39. The process according to claim 29, wherein said catalyst is
formed in situ inside the reactor.
40. The process according to claim 29, wherein said linear
polyethylene has a weight average molecular weight M.sub.w ranging
from 20,000 to 500,000 and a MWD (M.sub.w/M.sub.n) distribution
ranging from 2.5 to 4.
Description
[0001] This is a continuation application of U.S. application Ser.
No. 13/649,248 filed on Oct. 11, 2012, which is a divisional
application of U.S. application Ser. No. 10/578,873, filed Dec. 15,
2006, which is a 371 of PCT/EPO4/12746 filed on Nov. 9, 2004.
[0002] The present invention relates to an improved solid component
of catalyst for the (co)polymerization of ethylene and the
(co)polymerization processes in which said component is used.
[0003] More specifically, the present invention relates to a solid
component of catalyst and the catalyst obtained therewith, based on
titanium, magnesium and chlorine, possibly also comprising an inert
solid, suitable for effecting polymerization and copolymerization
processes of ethylene, especially in gas phase, to obtain linear
polyethylenes, preferably having low to ultra-low density.
[0004] As is known, linear low density polyethylenes (also referred
to as LLDPE) form a group of thermoplastic polymers widely used in
numerous practical applications, due to their good combination of
rheological, mechanical and thermal properties which make them
suitable for processing in the molten state for the manufacturing
of mono- and multi-layer sheets and films having a good
weldability, resistance to tear and perforation, flexibility and
transparency. These polyethylenes consist of ethylene copolymers
with quantities varying from 0.1 to 20% in moles of one or more
other monomers (comonomers) selected from primary alpha-olefins
having from 4 to 10 carbon atoms, sometimes also containing
propylene in much lower amounts with respect to said alpha-olefins.
They are obtained by means of accurately selected variants of the
Ziegler-Natta polymerization process, by polymerizing ethylene in a
mixture with suitable quantities of the desired comonomer(s), so
that, on the basis of the relative reactivity ratios and other
factors depending on the characteristics of the catalyst and
process conditions, a certain quantity of the above alpha-olefins
is inserted in the chain formed by the ethylene monomeric units. On
the basis of the quantity and type of comonomer inserted and its
distribution, which is seldom completely statistic, LLDPE are
obtained with different properties.
[0005] Methods and further details of what is specified above can
be easily found in the enormous quantity of publications on the
subject, among which, the treatise "Encyclopedia of Polymer Science
and Engineering", John Wiley & Sons Ed, Second Edition (1986),
volume 6, pages 429-453, can be mentioned, for example.
[0006] Ziegler-Natta catalysts suitable for forming substantially
linear ethylene copolymers, having a high molecular weight,
generally consist of a solid component, comprising a compound of
the elements of group 4 to 6 of the periodic table, preferably
titanium, vanadium or chromium, in contact with an aluminum alkyl
or an aluminum alkyl chloride. Numerous variations and alternatives
have been proposed, among which the introduction of an active
catalyst support, consisting of magnesium dichloride with a complex
morphology, is particularly important.
[0007] U.S. Pat. No. 3,642,746, for example, describes a solid
component of catalyst obtained by contact of a transition metal
compound with magnesium chloride treated with an electron donor.
According to the U.S. Pat. No. 4,421,674 a solid component of
catalyst is obtained by contact of a transition metal compound with
the spray drying product of a solution of magnesium chloride in
ethanol.
[0008] According to patent UK 1,401,708 a solid component of
catalyst is obtained by interaction of a magnesium halide, a
non-halogenated transition metal compound and an aluminum halide.
U.S. Pat. Nos. 3,901,863 and 4,292,200 describe solid components of
catalyst obtained by putting a non-halogenated magnesium compound,
a non-halogenated transition metal compound and an aluminum halide
in contact with each other. The product thus obtained is a mixed
chloride whose crystalline structure has lattice imperfections
which are suitable as polymerization active centres of ethylene and
alpha-olefins.
[0009] U.S. Pat. No. 4,843,049 and European patent application
EP-243,327, describe a solid component of catalyst containing
titanium, magnesium, aluminum, chlorine and alkoxyl groups, highly
active in ethylene (co)polymerization processes, carried out at low
pressure and temperature, through the suspension technique and,
respectively, at high pressure and temperature, in vessel or
tubular reactors. These solid components are generally obtained by
spray drying an ethanolic solution of magnesium chloride to obtain
an active support which reacts in sequence with a titanium
tetra-alkoxide or with titanium tetrachloride and aluminum alkyl
chloride, respectively.
[0010] The paper published in "Polymer" vol. 34(16), 1993, pages
3514-3519, shows the effect of the addition of certain amounts of
protic compounds to the co-catalyst, consisting of an aluminum
trialkyl, in the formation of solid polymerization catalysts based
on Ti and Hf supported on magnesium chloride. A decrease in the
activity is generally observed together with an increase in the
molecular weight of the polymer obtained.
[0011] Catalysts are also known in the known art, in which the
transition metal compound is fixed to a solid carrier, of an
organic or inorganic nature, optionally physically and/or
chemically treated so as to obtain a suitable morphology. Examples
of these solid carriers are oxygenated compounds of bivalent metals
(such as oxides, oxygenated and carboxylated inorganic salts), or
hydroxy chlorides or chlorides of bivalent metals, especially
magnesium chloride.
[0012] Solid components of catalyst obtained by activating a
complex containing magnesium, titanium, halogen, alkoxyl groups and
an electron donor, with an aluminum halide, are particularly known
in the art. This kind of complex can be deposited on a carrier,
especially a porous carrier and then activated to give solid
components of catalyst which are particularly suitable for the
polymerization or copolymerization of ethylene in gaseous phase.
For this known art, reference should be made to what is described
and illustrated in patents U.S. Pat. No. 4,293,673, U.S. Pat. No.
4,302,565, U.S. Pat. No. 4,302,566, U.S. Pat. No. 4,303,771, U.S.
Pat. No. 4,354,009, U.S. Pat. No. 4,359,561, U.S. Pat. No.
4,370,456, U.S. Pat. No. 4,379,758, U.S. Pat. No. 4,383,095 and
U.S. Pat. No. 5,290,745.
[0013] Even if these processes and catalysts allow polyethylenes to
be obtained in granular form with a good industrial productivity,
thanks to the polymerization carried out in gas phase, they have
proved to be not completely satisfactory as far as the rheological
characteristics of the particulate are concerned, due to the
presence of fine products, the friability of the granules and a
certain residual tackiness, which tend to produce clotting areas.
It would be desirable, moreover, to further improve the
productivity of these processes, in terms of amount of polymer
obtained per unit of weight of catalyst.
[0014] A further problem deriving from the residual tackiness of
certain polyethylenes, especially linear low density polyethylenes
(LLDPE), which has been observed, relates to the transportation,
storage and subsequent processing of these materials both in
granular form, due to the possible formation of blocks and clots,
and in the form of films, due to the difficulty of separating and
unrolling the bobbins of film.
[0015] Particularly serious drawbacks are encountered when the
above processes in gas phase are used for the production of linear
polyethylenes having a density equal or below 0.915 g/ml,
especially between 0.900 and 0.912 g/ml, which are widely used in
the film area. In this case, in fact, there is not only an increase
in problems relating to the residual tackiness of the granulate,
which tends to become deformed and to clot, making transportation,
storage and subsequent material processing operations difficult due
to the possible formation of clots, or as a result of the
difficulty in separating and unrolling the film bobbins, but the
polymerization step itself is carried out with a certain
difficulty, and is almost impracticable on an industrial scale
below a density of 0.910, due to the weight increase of the fluid
bed, until its possible collapse. For this reason, the production
of LLDPE having a density below 0.915 (also known as VLDPE) is
still mainly achieved with suspension, solution or high-pressure
processes, in which, however, there are still drawbacks relating to
the use of a liquid medium acting as diluent.
[0016] A process and catalyst capable of producing polyethylenes
within a low or very low density range, having such characteristics
as to allow the gas phase method to be adopted, would undoubtedly
represent a considerable improvement. It would also be highly
desirable to achieve a high productivity of the process, to
increase the product volumes and reduce the amount of residual
impurities of the catalyst.
[0017] It has now been found that it is possible to obtain solid
components of Ziegler-Natta catalyst on a carrier prepared from a
magnesium chloride made soluble in a polar compound, by means of a
simple and convenient process which allows catalysts to be obtained
with an improved catalytic activity and selectivity to give a
copolymer of ethylene having excellent rheological and mechanical
properties and an extremely reduced residual tackiness, even after
long storage times at temperatures up to 50.degree. C. In
particular, it has been found that significant lower tackiness is
obtained for linear polyethylenes having density equal to or lower
than 0.950 g/ml, and further, the achievement of polyethylenes with
densities as low as from 0.900 to 0.915 g/ml has been made
available by a gas phase process.
[0018] In accordance with this, the present invention relates to a
solid component of catalyst for the (co)polymerization of ethylene,
comprising titanium, magnesium, chlorine, an organo-oxygenated
protic compound D.sub.p and a neutral electron-donor aprotic
compound D, in the following molar ranges: [0019] Mg/Ti=1.0-50;
D/Ti=1.0-15; [0020] Cl/Ti=6.0-100; D.sub.p/D=0.05-3.
[0021] Said solid component can be advantageously obtained by means
of a process which forms a second object of the invention,
comprising the following steps in succession:
(a) formation of a mixture and dissolution, in said electron-donor
aprotic compound D, of a magnesium chloride and a titanium compound
having formula (I):
Ti.sup.v (OR.sup.3).sub.aX.sub.(v-a) (I) [0022] wherein each
R.sup.3 represents a hydrocarbyl or acyl radical having from 1 to
15 carbon atoms; [0023] each X is selected from chlorine, bromine
or iodine; [0024] v is 3 or 4, and represents the oxidation state
of titanium, [0025] a is a number varying from 0 to v, [0026] with
a molar ratio between magnesium and titanium ranging from 1/1 to
50/1; (b) partial separation of the compound D from said mixture
prepared in step (a) until a residue is obtained, solid at room
temperature, wherein the D/Ti ratio ranges from 1.5 to 40, (c)
formation of a suspension of said solid residue in an inert liquid
medium, preferably hydrocarbon, (d) addition to said suspension of
an organo-oxygenated protic D.sub.p, in such a quantity that the
molar ratio D.sub.p/D ranges from 0.1 to 1.2, preferably from 0.2
to 1.2, and maintaining the mixture until the desired solid
component of catalyst is formed.
[0027] According to a preferred embodiment, an inert solid I is
also added to the solution in (a), in a suitable granular form,
having the function of carrier and/or favouring the production of
the desired morphology in the solid component of the present
invention.
[0028] The solid component according to the present invention
allows catalysts to be obtained, with an extremely high activity,
but above all selective towards the formation of ethylene polymers
and copolymers with a morphology, molecular weight distribution and
the possible comonomer in the chain resulting in the complex in a
combination of highly desirable properties such as: excellent
rheology, with a shear sensitivity according to ASTM D1238-01, at
least higher than 20, and preferably ranging from 25 to 40; a high
mechanical resistance, tear resistance, tensile strength,
perforation resistance; a low residual tackiness of the film. For
this purpose, said solid component must be subjected to an
activation process by contact and reaction with aluminum alkyls, in
one or more steps, before enabling the formation of the desired
polymerization catalyst.
[0029] As is customary, in accordance with the present patent
application, any reference to elements, radicals, substituents,
compounds or parts thereof, included in a group, also comprises
reference to any mixture of elements of the group with each
other.
[0030] Said solid component is preferably characterized by the
following molar ratio ranges among the constituents: [0031]
Mg/Ti=1.5-10; D/Ti=3.0-8.0 [0032] Cl/Ti=10-25;
D.sub.p/D=0.1-2.0.
[0033] Even more preferably, said D.sub.p/D ratio ranges from 0.2
to 1.0.
[0034] The titanium can be present in the solid component in
oxidation state +3 or +4, or also as a mixture of compounds in the
two oxidation states. The oxidation state generally depends on the
preparation method used.
[0035] According to a preferred embodiment, from 10 to 90%,
preferably from 20 to 70% by weight of the solid component can
consist of said inert solid I, the remaining percentage being the
catalytically active part. The inert solid can be conveniently
included in the solid component, by introducing it, in the desired
proportions, during step (a) of said preparation method.
[0036] The aprotic electron-donor compound D can be any organic
compound, liquid under the process conditions of step (a), having a
coordinating capacity due to the presence of a heteroatom selected
from non-metallic compounds of groups 15 and 16, preferably an
organic compound having from 3 to 20 carbon atoms, preferably from
4 to 10, more preferably containing at least one oxygen atom linked
to a carbon atom. Compounds D are those belonging to the groups of
ketones, ethers, esters, amines, amides, thio-ethers and xanthates,
aliphatic or aromatic, linear or cyclic. Ethers, ketones and
esters, especially cyclic ethers are preferred. Typical examples
are dibutyl ether, dihexyl ether, methyl ethyl ketone, diisobutyl
ketone, tetrahydrofuran, dioxane, ethyl acetate, butyrolactone or a
mixture thereof.
[0037] The protic organo-oxygenated compound D.sub.p, according to
the present invention, is a compound capable of releasing an acid
proton under medium-high basicity conditions, for example a
compound with pKa 16. D.sub.p is preferably selected from compounds
having the following formula (II):
R-(A).sub.m-OH (II)
wherein: [0038] R is an aliphatic, cyclo-aliphatic or aromatic
radical, optionally fluorinated, containing from 1 to 30 carbon
atoms, [0039] A is selected from divalent groups having the formula
CR.sup.1R.sup.2, CO, SCO and SO, preferably CO or CR.sup.1R.sup.2,
wherein each R.sup.1 and R.sup.2 is independently hydrogen or an
aliphatic or aromatic group having from 1 to 10 carbon atoms, more
preferably CO [0040] m is 0 or 1.
[0041] In particular said D.sub.p is selected from alcohols and
organic acids, aliphatic or aromatic, preferably aliphatic having
from 2 to 10 carbon atoms. Typical examples of compounds suitable
for the purpose are: ethyl alcohol, butyl alcohol, hexyl alcohol,
isobutyl alcohol, amyl alcohol, benzyl alcohol, phenol, phenyl
butyl alcohol, decyl alcohol, neopentyl alcohol, cyclohexyl
alcohol, ethylene glycol, propylene glycol, diethylene glycol,
diethylene glycol monomethyl ether, acetic acid, propionic acid,
benzoic acid, hexanoic acid, 2-ethyl hexanoic acid, versatic acid
(mixture of acids), phenyl butyric acid, adipic acid, succinic acid
monomethyl ester, or mixtures thereof.
[0042] The process for the preparation of said solid component of
catalyst comprises a first step (a) in which a mixture of the
titanium compound having formula (I) and magnesium dichloride is
prepared in a liquid comprising the electron donor compound D. The
atomic ratio between magnesium and titanium is substantially the
same as the desired solid component, i.e. ranging from 1.0 to 50.
The donor compound D is introduced into the mixture in a quantities
which are at least sufficient to dissolve most of the above
compounds during step (a). It is generally preferable for at least
50% of said compounds to be dissolved, more preferably at least
80%, an it is even more preferable for the whole amount of
magnesium chloride to be brought to solution. D/Ti molar ratios
ranging from 5 to 100, are preferably used, more preferably from 10
to 50.
[0043] The titanium compound having formula (I) used for obtaining
the present solid component of catalyst is suitably selected so as
to be at least partially soluble in the electron-donor compound D
under the process conditions adopted in step (a). The R.sup.3 group
is preferably selected from aliphatic alkyl or acyl groups having
from 2 to 15, more preferably from 3 to 10 carbon atoms. X is
preferably chlorine. Suitable titanium compounds are chlorides and
bromides, for example TiCl.sub.4, TiCl.sub.3, TiBr.sub.4, and
titanium alcoholates or carboxylates. Examples of titanium
tetra-alcoholates suitable for the purpose are titanium
tetra-n-propylate, titanium tetra-n-butylate, titanium
tetra-iso-propylate and tetra-iso-butylate. Examples of
carboxylates are titanium tetra-butyrate, titanium tetra-hexanoate,
titanium versatate, and mixed compounds such as titanium dichloride
dihexanoate or titanium trichloride acetate.
[0044] Titanium trichloride is a solid compound less soluble in the
donor compounds D, with respect to TiCl.sub.4, but it has been
found that it is still suitable for the formation of the desired
solid component, even if it is not completely dissolved in step
(a).
[0045] The magnesium chloride introduced in step (a) can be in any
crystalline form, amorphous or mixed. Anhydrous magnesium chloride
is preferably used. Amorphous or semi-amorphous MgCl.sub.2 can be
obtained with different known methods, for example by spray-drying
from solutions in an alcohol, for example ethyl or butyl alcohol.
The magnesium chloride thus obtained can contain a residual
quantity of alcohol, normally less than 5% by weight, and is more
rapidly soluble in the donor D.
[0046] According to a particular embodiment, the magnesium chloride
introduced in step (a) can be at least partially formed in situ in
the same step (a), by the reaction of metallic magnesium with a
titanium +4 compound, preferably titanium tetrachloride, which is
correspondingly reduced to Ti+3. In this case, the reaction mixture
is preferably filtered before the addition of the constituents is
completed in step (a). A technique of this kind is described, for
example, in the above patent U.S. Pat. No. 5,290,745.
[0047] The order of addition of the components in the preparation
of the mixture of step (a) is not relevant. Both the Ti compound
and MgCl.sub.2 can be optionally introduced into the mixture in the
form of a solution in a suitable compound D, which may also not be
the same. The donor compound D can, if necessary, also be mixed
with a different inert liquid, such as, for example, un aromatic
hydrocarbon, normally up to a volume ratio of 1/1.
[0048] Step (a) conveniently comprises maintaining the mixture
formed as above at a temperature ranging from room temperature to
the boiling point of the donor compound D, typically from 50 to
120.degree. C., for a time varying from a few minutes to 24 hours,
in order to dissolve the maximum possible quantity of said Ti and
Mg compounds.
[0049] According to a particularly preferred aspect of the present
invention, the mixture obtained at the end of step(a) can also
comprise, in suspension, a quantity of inert solid I in granular
form, which can have various functions such as, for example,
improving the mechanical properties of the catalyst granule,
supporting the catalytic solid in order to increase the catalytic
surface effectively available, or it can act as a thickening agent
in the subsequent step (b) for the preparation of the catalytic
solid. Inert solids suitable for the purpose are certain polymers
in granule or powder form such as polystyrene or polyester,
possibly modified according to the known art.
[0050] Inorganic solids such as natural or synthetic silica are
preferably used, in its various varieties, also commercially
available, titania, silico-aluminates, calcium carbonate, magnesium
chloride (in a substantially insoluble form), or a combination
thereof. Said inert solids I are preferably in granular form with
average granule sizes ranging from 10 .mu.m to 300 .mu.m, and a
narrow size distribution. A silica typically suitable for the
purpose is a microspheroidal silica (size 20-100 .mu.m) having a
BET surface area ranging from 150 to 400 m.sup.2/g, a total
porosity equal or higher than 80% and an average pore radius of 50
to 200 .ANG..
[0051] The quantity of inert solid added to the mixture in (a) is
generally selected by normal experts on the basis of the role of
the inert solid in the catalyst or in its preparation. Such
quantities are conveniently used as to obtain at the end of the
preparation a content of inert product ranging from 10 to 90%,
preferably from 20 to 70%, by weight with respect to the total
weight of the solid component. In particular, if the inert solid is
mainly introduced as a thickening agent, such quantities as to
obtain a final content of inert product of 25 to 50% by weight, are
preferred. If the inert solid is mainly used as a carrier, the
quantity in the end-product preferably varies from 40 to 60% by
weight.
[0052] The procedure for introducing the inert solid I in the
mixture of step (a), is not critical. The solid can be added to the
donor D before the other compounds, or after their dissolution and
possible filtration of the solution. In a preferred embodiment, the
inert solid, particularly silica, is put in suspension in a part of
the compound D and optionally heated for a few minutes under
stirring, before being added to the mixture containing the Ti and
Mg compounds and the remaining quantity of D.
[0053] At the end of step (a), the mixture obtained is separated in
step (b) from most of the electron-donor compound D, until the
desired D/Ti molar ratio is obtained, by means of any of the
techniques of the art suitable for the purpose, for example by
precipitation by the addition of an excess of a hydrocarbon
compound, such as hexane or heptane, or by evaporation. A residue
is obtained at the end, either solid or with a pasty
consistency.
[0054] Any evaporation technique can be used for the purpose, such
as flash evaporation, distillation, current evaporation,
spray-drying, the latter being preferred. In an embodiment,
evaporation by means of spray-drying comprises heating the mixture
(solution or suspension) to a temperature close to boiling point
and forcing it through a nozzle into a chamber operating below
atmospheric pressure, or in which an inert gas is circulated. In
this way, granules are obtained, having the desired size, generally
with a diameter ranging from about 10 to about 200 .mu.m.
[0055] In the solid obtained at the end of said step (b),
essentially all the titanium is adsorbed and physically dispersed
on the magnesium chloride.
[0056] In the subsequent step (c), the residue of step (b) is added
to an inert liquid in which the solid part is essentially
insoluble. Suitable inert liquids are generally hydrocarbons,
optionally halogenated, for example fluorinated, in particular
aliphatic, cyclic or linear hydrocarbons such as hexane,
cyclohexane, heptane, decane, etc.
[0057] If an inert liquid has been introduced in step (a), it can
be evaporated together with the compound D, or, especially if it is
higher boiling than D, it can partly remain in the mixture with the
solid residue, thus directly forming the suspension obtained at the
end of step (c). The quantity of liquid in step (c) is not critical
but the solid/liquid ratio can conveniently range from 10 to 100
g/l.
[0058] It has been found that the donor compound D remains stably
bound to the above solid residue, under normal temperature
conditions, and is not removed in significant quantities by washing
with an inert liquid such as that used for the suspension in step
(c).
[0059] According to a particular aspect of the present invention,
the solid residue obtained in the above step (b), or also the
suspension in the inert liquid of step (c), can be obtained as
described in patents U.S. Pat. No. 4,302,566, U.S. Pat. No.
4,354,009 or U.S. Pat. No. 5,290,745, whose contents are
incorporated herein as reference, in particular in relation to the
preparation of the so-called "precursor".
[0060] Consequently, the solid component according to the present
invention can also be obtained by modifying in accordance with said
step (d) or said steps (c) and (d) in succession, a solid catalyst
precursor, comprising titanium, magnesium, chlorine, an aprotic
electron-donor compound
[0061] D and optionally an inert solid compound I, in which the
constituents are in the following molar ratios: [0062] Mg/Ti=1-50;
D/Ti=2.0-20; Cl/Ti=6-100; preferably [0063] Mg/Ti=1.5-10;
D/Ti=4.0-12; Cl/Ti=10-30; and said inert solid I is in a quantity
ranging from 0 to 95%, preferably from 20 to 60% by weight with
respect to the total weight of the precursor.
[0064] In step (d) of the process according to the present
invention, a protic compound D.sub.p containing at least one
hydrogen atom with acid or weakly acid characteristics, as defined
above, is added to the suspension obtained according to said step
(c). Said compound D.sub.p is added in such a quantity that the
molar ratio with the electron-donor compound ranges from 0.1 to
1.2, preferably from 0.2 to 1.2, even more preferably from 0.3 to
0.7.
[0065] The organo-oxygenated protic compound D.sub.p reacts with
the solid present in the suspension partly substituting the donor D
until equilibrium is reached, i.e. when the D.sub.p/D ratio in the
liquid remains constant. The compound D.sub.p is preferably added
in a molar quantity equal to or lower than the quantity of D
effectively bound to the solid obtained in step (c), or in any case
to the solid precursor. The reaction is conveniently carried out by
heating the mixture to a value ranging from 40 to 100.degree. C.,
more preferably from 60 to 80.degree. C., for a period varying from
5 minutes to 5 hours. The reaction generally reaches equilibrium in
times of less than 60 minutes.
[0066] In a preferred embodiment, the protic compound D.sub.p is
added to the suspension at room temperature, and the suspension is
then heated to the desired temperature for 20-40 minutes, under
stirring.
[0067] Said solid component of catalyst preferably consists of at
least 90% by weight, more preferably at least 95% by weight of said
components of Ti, Mg, Cl, D, D.sub.p and optionally the inert
solid. If the titanium and magnesium compounds introduced in step
(a) are essentially chlorides, the solid component obtained even
more preferably substantially consists of said components. If, on
the other hand, carboxylates or alcoholates are at least partially
used in step (a), the oxygenated protic compound D.sub.p in the
end-product can also represent a mixture of compounds different
from the compound having formula (II) introduced in step (d), due
to exchange with said carboxylates or alcoholates. In any case,
however, the beneficial effects due to the presence of said
organo-oxygenated protic compound as a whole are not modified.
[0068] All of the above operations for the preparation of the solid
component of catalyst are conveniently carried out in a controlled
and inert atmosphere, for example of nitrogen or argon, depending
on the sensitivity of aluminum alkyls and solid component of
catalyst to air and humidity.
[0069] The quantity of titanium contained in the solid component of
the present invention preferably does not exceed 10% by weight, and
more preferably ranges from 1 to 5% by weight. Titanium contents
higher than 10% by weight do not offer any further advantage in
terms of catalytic activity, presumably due to the fact that the
additional titanium is present in the solid in an inactive form or
is unavailable to interact with the olefin to be polymerized.
[0070] The solid component of catalyst thus obtained can be
separated from the liquid by means of the known liquid/solid
separation means suitable for the purpose, such as decanting,
filtration, centrifugation, or a combination of these, with the
exception of evaporation of the solvent.
[0071] It is subsequently washed with a hydrocarbon solvent and
optionally dried, or maintained in suspension in said solvent.
[0072] The solid component of catalyst thus obtained forms an
excellent catalyst for the (co)polymerization of a-olefins combined
with a suitable activator and/or co-catalyst, consisting of an
alkylic organometallic compound of aluminum, preferably an aluminum
alkyl or an aluminum alkyl halide.
[0073] In particular, in a preferred embodiment of the present
invention, said solid component is first activated by contact and
reaction with a suitable quantity of an aluminum alkyl or alkyl
chloride and the activated solid component subsequently forms the
final catalyst by contact and reaction with a suitable quantity of
aluminum trialkyl. According to this preferred embodiment, the
solid component is put in contact and reacted, in a suitable inert
liquid medium, with an aluminum alkyl or alkyl chloride represented
by means of the following general formula (III):
AlR'.sub.nX.sub.(3-n) (III)
wherein: R' is a linear or branched alkyl radical containing from 1
to 20 carbon atoms, X is selected from H and Cl, preferably Cl, and
"n" is a decimal number having values ranging from 1 to 3,
preferably from 2 to 3; in such a quantity that the Al/(D+D.sub.p)
ratio ranges from 0.1 to 1.5, preferably from 0.2 to 1.3, even more
preferably from 0.3 to 1.0.
[0074] Aluminum alkyl chlorides having formula (III) are known and
widely used in the field of the polymerization of olefins.
Preferred aluminum alkyl chlorides are compounds having formula
(III) wherein R' is a linear or branched aliphatic radical, having
from 2 to 8 carbon atoms. Typical examples of these compounds are
ethyl aluminum dichloride, diethyl aluminum chloride, ethyl
aluminum sesquichloride, isobutyl aluminum dichloride, dioctyl
aluminum chloride. Alkyl aluminum chlorides having non-integer
decimal values of "n" can be obtained, according to the known art,
by mixing, in suitable proportions, aluminum chlorides and aluminum
trialkyls and/or the respective mixed alkyl chlorides having "n"
equal to 1 and 2.
[0075] Aluminum alkyls included in said formula (III) are also
known, many of which are products available on the market. Typical
examples of these aluminum alkyls are aluminum trialkyl, such as
aluminum trimethyl, aluminum triethyl, aluminum triisobutyl,
aluminum tributyl, aluminum trihexyl, aluminum trioctyl, and
aluminum alkyl hydrides such as diethyl aluminum hydride, dibutyl
aluminum hydride, dioctyl aluminum hydride, butyl aluminum
dihydride.
[0076] The organometallic compound of aluminum having formula (III)
can be added as such, or in the form of a solution in an inert
organic solvent selected from hydrocarbons liquid at room
temperature, for example hexane, heptane, toluene, or also in
supported form on an inert solid analogous to the above solid
I.
[0077] According to a preferred aspect of the present invention,
especially for a subsequent use in the production of LLDPE, the
activation phase of said solid component can be effectively carried
out in two steps with two different organometallic compounds of Al
having formula (III). In the first step it is reacted with aluminum
trialkyl (n=3 in formula (III)), whereas in the second step it is
reacted with an aluminum dialkyl chloride (n=2, X=Cl, in formula
(III)), in such a quantity that the overall molar ratio
Al/(D+D.sub.p) ranges from 0.1 to 1.3, preferably from 0.4 to 1.1.
The solid component is normally not separated between the first and
second step. Also at the end of the activation it is preferable to
leave the activated component in suspension in the liquid reaction
medium possibly containing the aluminum alkyl or non-reacted alkyl
halide.
[0078] In another preferred aspect, in said first step the
AlR.sub.3/(D +D.sub.p) ratio ranges from 0.1 to 0.4, and in the
second step the AlR.sub.2Cl/(D +D.sub.p) ratio ranges from 0.2 to
0.7.
[0079] The activated catalyst component, obtained with the above
process contains at least 20% of titanium in reduced form
(oxidation state +3) with respect to the total quantity of
titanium. The titanium in reduced form is preferably at least 50%
of the total titanium, more preferably 80%. The quantity of
titanium +3 generally increases with an increase in the quantity of
aluminum alkyl having formula (III) reacted with the solid
component, and can be consequently regulated on the basis of the
experience of the expert in the art.
[0080] The solid component, both in activated and non-activated
form, is capable of forming a catalyst for the (co)polymerization
of a-olefins, and specifically ethylene, by contact and reaction
with a suitable co-catalyst.
[0081] Suitable co-catalysts which can be used in a combination
with the solid component activated as described above, are those
normally used in the art for the preparation of Ziegler-Natta
catalysts, particularly comprising a hydrocarbyl compound of a
metal selected from Al, Ga, Mg, Zn and Li, preferably aluminum,
more preferably aluminum trialkyls containing from 1 to 10, even
more preferably from 1 to 5, carbon atoms in each alkyl group.
Among these, aluminum trimethyl, aluminum triethyl, aluminum
tri-n-butyl, aluminum triisobutyl, are specially preferred.
[0082] In the catalysts of the present invention, the atomic ratio
between metal (in the co-catalyst) and titanium (in the solid
component of catalyst) generally varies from 10:1 to 500:1 and
preferably from 50:1 to 200:1, in relation to the particular
polymerization system adopted and the process parameters. If the
solid component is not activated, it is preferable to use a
metal/Ti ratio of at least 100 and up to 400, whereas the activated
component is preferably treated with an atomic ratio metal/Ti
ranging from 50:1 to 200:1.
[0083] Said catalyst is formed according to the known techniques,
by contact between the solid component and co-catalyst, by reacting
the components as such or in a suitable liquid medium, usually a
hydrocarbon, preferably the same in which the activated solid
component was obtained, in order to avoid the separation of the
suspension from the liquid. The concentration of co-catalyst in the
liquid medium is selected on the basis of normal practice and
generally ranges from 0.1 to 1.0 moles/L. The temperature at which
the catalyst is prepared, is not particularly critical, and is
preferably within the range of 0.degree. C. to the operating
temperature of the catalyst in the polymerization process, i.e. up
to a temperature of 120.degree. C. and even over.
[0084] The formation of the catalyst is normally extremely rapid
already at room temperature. The contact between the components is
usually selected from 5 seconds to 30 minutes, depending on the
temperature, before starting the polymerization. According to the
operating requirements, the catalyst can be formed in situ in the
polymerization reactor, or fed to the reactor after being preformed
in a suitable apparatus. In particular, in the case of
polymerization in gas phase, especially with the fluid bed
technique, it is preferable to feed the activated solid component
to the reactor separately from the solution of co-catalyst, forming
the catalyst directly in the polymerization environment. In this
case, the contact time is determined by the process conditions of
the fluid bed and is within the range of a few seconds to
approximately one minute.
[0085] The non-activated solid component can also be used for the
preparation of polymerization catalysts by means of contact and
reaction with a suitable quantity of co-catalyst, or an aluminum
trialkyl as specified above. In this case, the activation takes
place contemporaneously with the formation of the catalyst, using
the same aluminum alkyl, but it has been found in practice that a
catalyst with the same characteristics as that produced in two
separate steps, as described above, is not necessarily obtained,
even if the components used are identical. It has been found that
the polymerization catalyst prepared without the intermediate
activation step, which represents an object of the present
invention, is especially suitable for polymerization processes in
suspension.
[0086] A further object of the present invention relates to a
process for the (co)polymerization of ethylene, i.e. for the
polymerization of ethylene to give linear polyethylene and for the
copolymerization of ethylene with propylene or other
.alpha.-olefins, preferably having from 4 to 10 carbon atoms, which
comprises reacting ethylene and optionally at least one
.alpha.-olefin, under suitable polymerization conditions,
preferably in gas phase, in the presence of the above catalyst
according to the present invention. The quantity of catalyst is
generally selected by an expert in the field in order to allow the
process temperature to be controlled, i.e. so that the
polymerization is not excessively exothermic and does not cause the
softening and melting of the polymer granules. The amount of
catalyst introduced into the reactor is preferably selected so that
the titanium concentration ranges from 1 to 5 ppm by weight with
respect to the consolidated production.
[0087] Typical and non-limiting examples of polymerization process
conditions in gas phase, suitable for the use of the catalyst
according to the present invention, are described, with reference
to different catalysts, in the patents mentioned above, in
particular U.S. Pat. No. 4,302,566 and U.S. Pat. No. 4,293,673.
[0088] A polymerization process in gas phase according to the
present invention is conveniently carried out according to the
known fluid bed technique, by putting a gaseous stream of the
monomer(s) in contact with a sufficient quantity of the catalyst of
the present invention, at a temperature ranging from 70 to
115.degree. C., depending on the density of the (co)polymer to be
obtained (usually ranging for LLDPE from 0.90 to 0.95), and at a
pressure ranging from 500 to 1000 kPa.
[0089] The feeding stream of the monomers, to which that of the
recycled gases, from 30 to 50 times higher in volume, is added, is
sent to the bottom of the reactor through a distribution plate so
as to uniformly sustain, with efficient stirring, the suspended
catalyst bed and polymeric particulate in formation. A part of said
stream, or a secondary stream is preferably in liquid form with the
function of cooling, possibly by means of the presence of a
low-boiling inert liquid, for example hexane, to maintain the
desired temperature in the fluid bed.
[0090] The catalyst is preferably formed in situ, by introduction
in the fluid bed, through a stream of inert gas, of the activated
solid component in suspension, and co-catalyst, where it enters
into contact with the monomers coming from the bottom of the
reactor. The particle of polymer englobes the catalyst itself and
grows to the desired dimensions by contact with the monomers in gas
phase of the fluid bed.
[0091] Hydrogen or other known compounds suitable as chain transfer
agents can also be introduced at a suitable height of the reactor,
at times in the catalyst stream itself, in order to regulate the
average molecular weight to the desired value. Furthermore,
according to the gas phase polymerization technique in use, an
inert gas is also present in the gaseous mixture, usually nitrogen,
in an amount of 30% in volume.
[0092] The polymer thus produced is removed in continuous in the
lower area of the fluid bed and sent to the recovery section. The
catalyst is deactivated and the residual gases separated from the
polymer by means of a gaseous stream in a suitable flushing column.
Most of the un-reacted gas rises to the section of the reactor
above the fluid bed and is then sucked into a compressor and sent
back to the reactor as recycled product.
[0093] In accordance with what is specified above, the catalyst
according to the present invention can be used with excellent
results in normal industrial polymerization processes of ethylene
to give linear polyethylene and in the copolymerization of ethylene
with propylene or higher .alpha.-olefins, preferably having from 4
to 10 carbon atoms, to give copolymers having different
characteristics in relation to the specific polymerization
conditions and the quantity and structure of the .alpha.-olefin
itself. Linear polyethylenes can be obtained, for example, with
densities ranging from 0.890 to 0.970 g/cm.sup.3, preferably from
0.900 to 0.950 g/cm.sup.3, and with weight average molecular
weights M.sub.w, ranging from 20,000 to 500,000. .alpha.-olefins
preferably used in the copolymerization of ethylene for the
production of linear low or medium density polyethylene (known with
the abbreviations VLDPE or LLDPE), are 1-butene, 1-hexene and
1-octene. The .alpha.-olefin/ethylene molar ratio is selected, once
all the other conditions have been determined, on the basis of the
desired content of comonomer in the copolymer, and usually ranges
from 0.005 to 2.0, preferably from 0.1 to 1.0, even more
preferably, from 0.1 to 0.4.
[0094] The (co)polymers of ethylene thus obtained have excellent
mechanical and rheological characteristics, comparable to or even
higher than those of the best commercial polyethylenes having a
similar composition and density, but have a much lower tackiness,
expressed as gluing capacity, usually lower than 260 cN, preferably
ranging from 130 to 200 cN, whereas the polyethylenes obtained with
analogous processes, but in the presence of traditional catalysts,
produced from solid components containing only one type of
electron-donor compound, have gluing capacity values higher than
300 cN.
[0095] According to a particular embodiment of the present
invention, the said process for the copolymerization of ethylene
can be advantageously used for producing linear polyethylene having
a low to ultra-low density, namely below 0.915 g/ml, preferably
ranging from 0.900 to 0.915 g/ml, more preferably from 0.905 to
0.915 g/ml, by polymerization in gas phase, of a gaseous mixture
including ethylene and at least one alpha-olefin having from 4 to
10 carbon atoms, in the presence of the polymerization catalyst of
the present invention. Preferably, the polymerization process is
carried out at a temperature ranging from 70 to 95.degree. C.,
depending on the density of the (co)polymer to be obtained, and at
a pressure ranging from 300 to 3000 kPa, more preferably from 500
to 1000 kPa. The alpha-olefins preferably used for the production
of such linear low or very low density polyethylene (indicated as
LLDPE and VLDPE), are 1-butene, 1-hexene, 1-octene and mixtures of
said co-monomers, for example 1-hexene/1-butene in a molar ratio of
2/1. In some cases, polypropylene can also be suitably reacted, in
a molar ratio, with respect to ethylene, ranging from 0.1-0.3. The
alpha-olefin/ethylene molar ratio is selected by the technical
expert, once all the other conditions have been chosen, so as to
obtain, in the end, the desired co-monomer content in the
copolymer, and preferably ranges from 0.1 to 0.80, more preferably
from 0.1 to 0.4. In order to achieve the best performances of the
polyethylene thus obtained, the use of alpha-olefin/ethylene ratios
which increase (within the above-mentioned ranges) with an increase
in the molecular weight of the copolymer, has been found to be
convenient.
[0096] According to this embodiment, linear polyethylene is
obtained, having a density lower than 0.915 g/ml, a weight average
molecular weight M.sub.w ranging from 20,000 to 500,000, and an MWD
distribution (M.sub.w/M.sub.n) ranging from 2 to 7, preferably from
2.5 to 4. These ethylene copolymers show a morphology, molecular
weight distribution and distribution of the comonomer in the chain
which are such as to provide, in the complex, a combination of
highly desirable properties such as: excellent rheology, with a
shear sensitivity (usually SS, in short) according to ASTM
D1238-01, at least higher than 20, and preferably ranging from 25
to 40; a high mechanical resistance, tear resistance, tensile
strength, perforation resistance; a low residual tackiness in film
and granular form. In particular the reduced tackiness allows
control of the gas-phase process in such a way as to avoid any
undesired increase of the weight of the fluid bed and risk of
collapse.
[0097] The present invention is particularly illustrated in its
numerous aspects by the following examples which are provided for
solely illustrative purposes, and which should in no way be
considered as limiting the scope of the invention itself.
EXAMPLES
[0098] The following analytical and characterization methods were
used.
Melt Flow Index
[0099] The Melt Flow Index (MFI), correlated to the weight average
molecular weight of the polymer, measured according to the standard
ASTM-D 1238 E technique. The MFI is indicated, measured with a
weight of 2.16 kg at 190.degree. C., expressed as grams of polymer
melted in 10 minutes (g/10 min).
Shear Sensitivity, (SS)
[0100] Calculated as a ratio between the MFI at 2.16 kg and the MFI
at 21.6 kg, both measured according to the above standard
technique. This parameter is known to be correlated with the
molecular weight distribution.
Density
[0101] Determined according to the method ASTM D1505-98.
Residual Tackiness
[0102] Determined as a measurement of the gluing capacity according
to the method ASTM D5458-95
Dart
[0103] Determined according to the method ASTM D 1709-01 (Test
method B).
Perforation Resistance
[0104] Determined according to the method ASTM D5748-95
Elmendorf
[0105] Determined according to the method ASTM D1922-00
Reagents and Materials
[0106] The following reagents and materials were used in particular
in the practical embodiments object of the following examples.
Unless specified, the products were used as received from the
supplier.
[0107] Magnesium chloride ALDRICH (MgCl.sub.2, powder, purity
>99.9%); titanium trichloride ALDRICH (TiCl.sub.3 purity
>99.99%), 2-ethyl-hexanoic acid (purity 99.00%) produced by
BASF; 1-butanol ALDRICH (purity 99.8%); Tetrahydrofuran (THF)
ALDRICH (purity 99.9%); Diethyl Mono Chloro Aluminum (DEAC) (purity
99.90%); Tri-n-hexyl Aluminum (purity 99.90%), Triethyl Aluminum
(purity 99.90%), Trimethyl Aluminum (purity 99.90%), CROMPTON
products; n-heptane, produced by Synthesis-(PR) under the name of
SYNTSOL LP 7, purified by passage over molecular sieves.
Example 1
[0108] 30 ml of a suspension of heptane containing 1.0 g of a solid
precursor in powder form, prepared according to the method
described in U.S. Pat. No. 5,290,745 whose contents are integrally
included herein as reference, particularly example 1, paragraphs
(a) and (b) for the preparation of the solid precursor by the
spray-drying technique, are charged into a 200 ml glass vessel,
equipped with mechanical stirring and placed under inert atmosphere
of nitrogen. The precursor contained 660 mg of catalytically active
component comprising 0.51 mmoles of Ti, 2.82 mmoles of Mg, 7.17
mmoles of Cl, 4.34 mmoles of tetrahydrofuran (THF; electron-donor
compound D) and 340 mg of silica having the following
characteristics: average diameter 0.1 microns, porosity of 0.25
cc/g, surface area by means of B.E.T. 25 m.sup.2/g.
[0109] A further 70 ml of heptane are added, together with 0.2 ml
of 1-butanol (2.19 mmoles), and the suspension is left under
stirring for 20 minutes at room temperature. The temperature is
then brought to 70.degree. C. for 25 minutes, and the mixture is
subsequently cooled again to room temperature.
[0110] A suspension containing 1025 mg of solid component of
catalyst comprising the following constituents, was obtained: Ti
0.51 mmoles; Mg 2.82 mmoles; Cl 7.17 mmoles; silica 340 mg; THF
2.01 mmoles; BuOH 1.65 mmoles, with a molar ratio BuOH/THF in the
solid equal to 0.826. It is not separated from the suspension
liquid, but is directly subjected to activation by means of the
treatment described in the following example.
Example 2
[0111] The solid component obtained in example 1 is activated by
means of contact and reaction with a suitable quantity of an
aluminum alkyl in two subsequent steps.
[0112] 1.3 ml of tri-n-hexyl aluminum 1 M in heptane (THA; 1.3
mmoles), diluted in a further 10 ml approximately of heptane
(THA/(BuOH+THF) ratio=0.355), were added to 100 ml of the
suspension obtained in example 1, containing 1000 mg of solid
component, introduced into a glass container under nitrogen. The
whole mixture is left under stirring at room temperature for about
60 minutes, and 2.17 ml of diethyl aluminum chloride 1 M in heptane
(DEAC; 2.17 mmoles; DEAC/(BuOH+THF) ratio =0.593), are then added
at the same temperature, leaving the mixture under stirring for 60
minutes. A suspension of the activated solid component is obtained,
having a titanium concentration of 4.5 mmoles/l, which is directly
introduced into the polymerization reactor for the preparation of
the desired polyethylene.
Example 3
[0113] The procedure of the previous example 1 is exactly repeated,
but 0.35 ml of pure 2-ethyl-hexanoic acid (AEE; 2.19 mmoles) are
added instead of n-butanol, as protic compound D. At the end, 1064
mg of solid component of catalyst are obtained, in a heptane
suspension, comprising: Ti 0.50 mmoles; Mg 2.82 mmoles; Cl 7.17
mmoles; silica 339.88 mg; THF 3.39 mmoles; AEE 0.92 mmoles, with a
molar ratio on the solid AEE/THF=0.272.
Example 4
[0114] The solid component of catalyst obtained in the previous
example 3 is activated with the same procedure described in example
2, but using the following quantities of reagents:
1.3 ml of tri-n-hexyl aluminum 1M in heptane (1.3 mmoles) diluted
in about 10 ml of heptane (THA/(AEE+THF) ratio=0.302), 2.17 ml of
diethyl aluminum chloride 1 M (DEAC/(AEE+THF) ratio =0.503).
[0115] At the end a suspension is obtained comprising a
concentration of titanium equal to 4.4 mmoles/liter.
Example 5
[0116] The procedure of the previous example 1 is exactly repeated,
using the same reagents in the same quantities, with the only
difference that 0.1 ml of butanol (1.095 mmoles) are added to the
solid precursor suspension, instead of 0.2 ml. 952 mg of a solid
component of catalyst are obtained in the end, in a suspension of
heptane, comprising: Ti 0.50 mmoles; Mg 2.82 mmoles; Cl 7.17
mmoles; silica 340 mg; THF 2.83 mmoles, BuOH 0.825 mmoles, with a
molar ratio BuOH/THF in the solid matter equal to 0.291.
Example 6
[0117] The solid component, obtained as described in previous
example 5, is activated using a procedure similar to that indicated
in the previous example 2.
[0118] 0.87 ml of tri-n-hexyl aluminum 1 M in heptane (0.87
mmoles), diluted in a further 10 ml of heptane (THA/(BuOH+THF)
ratio =0.238) were added to 100 ml of the suspension obtained in
example 5, containing 952 mg of solid component, introduced in a
glass container under nitrogen. The mixture is left under stirring
at room temperature for about 60 minutes and, at the same
temperature, 2.17 ml of diethyl aluminum chloride 1 M in heptane
(DEAC: 2.17 mmoles; DEAC/(BuOH+THF) ratio=0.594) are added under
continual stirring for about 60 minutes. A suspension of the
activated solid component is obtained, with a titanium
concentration of 4.5 mmoles/l, which is used as such in the
polymerization reaction.
Examples 7-14
[0119] Polymerization of Ethylene. Various copolymerization tests
of ethylene (C.sub.2) were carried out with 1-hexene (C.sub.6), in
a gas-phase fluid-bed reactor, having a cylindrical geometry,
similar to the reactor illustrated and described in the
above-mentioned patents U.S. Pat. No. 4,302,565, U.S. Pat. No.
4,302,566, U.S. Pat. No. 4,303,771, whose contents are integrally
incorporated herein as reference, with a total internal volume of
2.33 m.sup.3. The reaction was carried out at an average
temperature of 84.degree. C. A gaseous stream containing ethylene
and 1-hexene is introduced from below by means of a distribution
plate with a gas surface rate of about 0.50 m/s. The
ethylene/1-hexene ratio is fixed as indicated in Table 1 below for
each test. Table 1 also indicates the fluid bed conditions (weight,
level and residence time expressed in terms of BTO, bed
turnover).
[0120] The suspension of the activated solid component, prepared as
described in the previous examples 2 or 4, is introduced laterally
into the reactor together with a solution of co-catalyst,
consisting of aluminum trimethyl (TMA) or aluminum triethyl (TEA)
at 5% by weight in hexane, with a flow-rate which is such as to
respect the atomic ratio Al/Ti according to what is specified in
Table 1.
[0121] The catalyst in its final activated form is formed by
reaction of the activated solid component and the co-catalyst in
situ directly in the fluid bed.
[0122] The polymer obtained in the form of a grossly spherical
particulate having the density and average diameter (APS) indicated
in Table 1, is continuously removed in the lower part of the
reactor, subjected to deactivation of the catalyst, separation of
the non-reacted monomers and sent to an extrusion-granulation
apparatus to obtain the product in granular form, suitable for
transportation and subsequent transformation. Table 1 indicates the
catalyst activity (in kg of polymer per gram of Ti in the catalyst)
for each test.
[0123] A part of the polymer is characterized for the rheological
properties (Melt Index MI and Shear Stress SS) and the density. A
part is subjected to filming using a blow extrusion apparatus Mod.
UNION TR60 with a Bielloni single-layer cast line to obtain films
suitable for measuring the mechanical properties (resistance to
perforation, dart and Elmendorf test (MD)). A part of the film is
measured to determine the gluing capacity according to the method
ASTM D5458-95 which is correlated to the residual tackiness.
Examples 15 and 16
(Comparative)
[0124] Two polymerization tests were effected with the same reactor
and under analogous conditions to those described in the previous
examples 7 to 14, using a catalyst obtained starting from the
non-modified solid component, prepared according to Example 1 of
the above patent U.S. Pat. No. 5,290,745, but activated repeating
the process of the previous example 2. The conditions adopted and
characteristics of the polymers obtained are summarized in Tables 1
and 2 below. On examining the data in Table 2, the surprising
reduction in the gluing capacity of the polyethylene can be
immediately observed (always lower than 190 cN) in all the examples
according to the invention, with respect to the values of 327 and
350 cN, characteristic of polyethylenes obtained with the process
based on traditional catalysts.
[0125] All the other characteristics are, on the contrary, in line
with the satisfactory values of traditional polyethylenes.
TABLE-US-00001 TABLE 1 Polymerization process Example 15 16 7 8 9
10 11 12 13 14 (Comp) (Comp) Solid component 2 4 4 4 4 4 2 2 -- --
of catalyst (Ex. Nr.) Pressure (kPa) 605 708 771 779 833 790 725
745 690 748 Aluminum alkyl TMA TEA TEA TMA TMA TMA TMA TMA TEA TMA
Al/Ti (atom/atom) 91 95 85 79 110 46 75 73 141.2 93.5
H.sub.2/ethylene 0.225 0.199 0.172 0.182 0.184 0.202 0.196 0.184
0.185 0.22 (mol/mol) Hexene/ethylene 0.149 0.177 0.163 0.151 0.154
0.161 0.145 0.138 0.140 0.153 (mol/mol) Bed weight (kg) 58 56 55 54
53 52 54 54 57.6 54.1 Bed level (m) 2.1 2.2 2.2 2.2 2.3 2.1 2.1 2.0
2.1 1.99 BTO (hr) 3.0 3.0 3.1 3.2 2.8 2.8 3.0 3.0 2.5 2.7
Production (kg/hr) 19.1 19.0 17.7 17.0 17.0 19.0 19.0 18.0 22.7 20
Activity (kg.sub.PE/g.sub.Ti) 1163 1170 1053 1015 1053 948 1068
1060 1290 910
TABLE-US-00002 TABLE 2 Polyethylene characterization Example 7 8 9
10 11 12 13 14 15 (comp) 16 (comp) MI (g/10 min) 2.55 2.67 2.56
2.63 2.46 2.48 2.60 2.55 2.83 2.51 Density (g/cm.sup.3) 0.9171
0.9175 0.9181 0.9167 0.9177 0.9173 0.9171 0.9182 0.9192 0.9169 S.S.
31.0 29.6 30.6 30.0 31.2 29.7 30.5 30.0 31.0 29.0 Bulk density
0.297 0.303 0.310 0.284 0.274 0.276 0.308 0.325 0.331 0.352
(g/cm.sup.3) APS (.mu.m) 566 620 617 651 643 670 536 540 513 563
Gluing capacity 183 172 158 181 183 166 176 169 327 350 (cN)
Perforation 1461 1461 1356 1501 1776 1642 1450 1536 1387 1450
(N/mm) Dart (J/mm) 35 43 41 50 33 50 44 42 33 37 Elmendorf MD 130
121 103 101 106 110 134 136 132 170 (N/mm)
Examples 17-23
(Co)Polymerization of Ethylene.
[0126] Various copolymerization tests of ethylene (C.sub.2) were
carried out with 1-hexene (C.sub.6), in the same gas-phase
fluid-bed reactor as described in previous example 7. The reaction
was carried out at an average temperature of 84.degree. C. A
gaseous stream containing ethylene and 1-hexene is introduced from
below by means of a distribution plate with a gas surface rate of
about 0.50 m/s. The ethylene/1-hexene ratio is fixed as indicated
in Table 3 below for each test. Table 3 also indicates the fluid
bed conditions (weight, level and residence time expressed in terms
of BTO, bed turnover).
[0127] The suspension of activated solid component, prepared as
described in the previous examples 2 or 6, is introduced laterally
into the reactor together with a solution of co-catalyst,
consisting of aluminum trimethyl (TMA) or aluminum triethyl (TEA)
at 5% by weight in hexane, with a flowrate which is such as to
respect the atomic ratio Al/Ti according to what is specified in
Table 3.
[0128] The catalyst in its final activated form is formed by
reaction of the activated solid component and the co-catalyst in
situ directly in the fluid bed.
[0129] The polymer obtained in the form of a grossly spherical
particulate having the density and average diameter (APS) indicated
in Table 3, is continuously removed in the lower part of the
reactor, subjected to deactivation of the catalyst, separation of
the non-reacted monomers and sent to an extrusion-granulation
apparatus to obtain the product in granular form, suitable for
transportation and subsequent transformation. Table 3 indicates the
catalyst activity (in kg of polymer per gram of Ti in the catalyst)
for each test.
[0130] A part of the polymer is characterized for the rheological
properties (Melt Index MI and Shear Stress SS) and the density. A
part is subjected to filming using a blow extrusion apparatus Mod.
UNION TR60 with a Bielloni single-layer cast line to obtain films
suitable for measuring the mechanical properties (resistance to
perforation and dart).
Example 24
[0131] (comparative)
[0132] A polymerization test was effected in the same reactor and
under analogous conditions as those described in the previous
example 17, using a catalyst obtained starting from the
non-modified solid component, prepared according to example 1 of
the above-mentioned patent U.S. Pat. No. 5,290,745, and activated
by repeating the process of the previous example 2. It was
impossible, however, to complete the polymerization test due to the
increasing heaviness of the bed, which, after a few minutes of
production, could no longer be sustained by the gas stream. This
result can be attributed to the excessive tackiness of the
copolymer thus produced, which tends to clot in the polymerization
reactor itself and is difficult to remove. The distinct technical
progress represented by the process of the present invention, is
therefore evident.
TABLE-US-00003 TABLE 3 Polymerization process and characterization
of products. Example 24 17 18 19 20 21 22 23 (comp.) Activat. solid
component 2 2 2 2 6 6 6 -- (preparative ex. number) Pressure (kPa)
516 553 676 673 535 550 520 535 Temperature (.degree. C.) 80 83 82
84 80 83 84 80 TEA/Ti (mol./atom) 61 61 70 60 48 47 45 63
H.sub.2/ethylene (mol/mol) 0.102 0.135 0.205 0.216 0.108 0.225
0.170 0.112 1-hexene/ethylene -- -- 0.163 0.149 -- 0.145 -- --
(mol/mol) 1-butene/ethylene 0.227 0.186 -- -- 0.215 -- 0.315 0.215
(mol/mol) Bed weight (kg) 49 50 48 52 54 56 56 >60 BTO (h) 2.3
2.4 2.3 2.4 2.6 2.7 2.6 n.d. Production (kg/h) 20.8 20.8 21 21.5
20.6 20.4 20 n.d. Activity (kg.sub.PE/g.sub.Ti.) 1080 1138 1054
1043 953 919 940 n.d. Density (g/cm.sup.3) 0.908 0.913 0.913 0.914
0.909 0.913 0.913 n.d. Apparent density (g/cm.sup.3) 0.269 0.270
0.274 0.298 0.300 0.340 0.302 n.d. MI (g/10 min) 1.0 1.17 2.97 3.43
0.98 3.08 1.3 n.d. S.S. 29.1 30.2 31.4 32 30.1 28.7 29.9 n.d.
Perforation (N/mm) 1048 1342 1337 1298 1050 1320 1315 n.d. Dart
(J/mm) 98 63 67 65 97 68 61 n.d. n.d.: not determined
* * * * *