Note: Descriptions are shown in the official language in which they were submitted.
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An object o~ the present invention is to provide
supports particularly suitable for the production of
catalysts for the low pressure polymerisation and
copolymerisation of ~-olefines. In such processes, the
catalytic system generally consists of a Ziegler catalyst,
for example a halogen of a transition metal and an organic
metal compound.
The transition metal may notably be fixed onto a
support such as A1203, aluminium silicates, SiO2,
MgO, MgC03 or Mg(OH)2-
Said low pressure polymerisation processes may also be
executed in the presence of catalytic complexes of the
TiC13. 1/3 AlC13 type, as described in British patent
1,268,415, and in U.S.A. patent 3,639,377.
Processes of this type have the advantage of easy
control of the average molecular weight of the product
polymers. However, they have a considerable drawback in
that the polymers generally require washing with alcoholic
solutions to separate them from the harmful residues of
the catalytic system.
Halogenation of the supports, for example A1203,
SiO2, MgO or SiO2.A1203, lead to a considerable
increase in the activity of the catalyst system, such that
it i5 possible to avoid the costly final wash of the
polymer (see for example, British patents 1,31~,78~, and
1,315,770).
Such catalysts however do not allow easy control of
the average molecular weight of the polymer, and the
products are therefore often difficult to work, having, in
general, very high average molecular weights and melt
indices approximately equal to zero (measured by the ASTM
D 1238 method, with a weight of 2.16 Kg).
We have now discovered a process for the polymerisation
and copolymerisation of ~-olefines, which combines the
advantages of both the aforementioned types of catalyst,
.e.:
a) high catalytic activity in polymerisation such that
it is possible to dispense with any washing of the
polymers obtained;
b) easy control of the average molecular weights of
the polymers.
The catalyst support used in this process, which
before use is reacted with a Ziegler catalyst, consists of
an aluminium compound of the formula (I).
lK (3K _ n) nH (I)
where:
X is a halogen atom or an inorganic oxygenated anion
such as a sulphate or nitrate);
m is the valency of the individual group X;
K is the number of aluminium atoms;
n is an integer from 0.01 to 3, and preferably from
0.05 to 3.
This support may be obtained from the corresponding
nonhydroxylated aluminium compound by subjecting it to
partial hydrolysis by the method described in detail below.
It may be mentioned that the best results are obtained
starting from aluminium halides, in particular AlF3.
Aluminium fluoride exists in three different allotropic
forms: ~-rhombic, ~-hexagonal and ~-tetragonal.
All three forms are very suitable for the preparation
of highly active supports. However, particularly good
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results have been obtained from the ~-hexagonal form.
The catalytic hydroxylated support is formed by
treating an aluminium hydride or an oxygenated inorganic
salt of aluminium (such as sulphate or nitrate) with any
compound able to partially hydrolyse it and thus introduce
hydroxyl groups therein. Water or aqueous ammonia are
preferred ~or this purpose, but other organic or inorganic
substances, either pure or in solution, have been found to
give good results.
The reaction between the aluminium compound of formula
AlX3 and the compound which is to introduce hydroxyl
groups therein may be carried out in a fixed or fluidised
bed.
In general, an inert gas is added. Examples include-
nitrogen; helium; argon; and air~ These gasses may be
completely or only partially saturated with the
hydrolysing compound. The critical conditions of the
partial hydrolysis reaction of the compound AlX3 are the
temperature and duration of treatment. By varying these,
the value of n varies in the following manner: as the
temperature and duration of treatment increase, n tends to
decrease until it reaches zero.
In the operating conditions of the invention the zero
value is never reached.
The treatment temperature may vary from 100 to 800C,
and preferably from 200 to 600C.
The duration of treatment may vary from l to 24 hours
and preferably from 4 to 12 hours.
The present invention provides a method for preparing
a wide range of catalytic supports for which the specific
activity of the final catalytic system, expressed as kg of
obtained polymer/g transition metal/hour/atmosphere of
olefine, varies as the value of n varies. A simultaneous
variation in the properties of the product polymer (such
as specific density, crystallinity, average molecular
weight and melt index) occurs enabling the preparation of
a wide variety of polymers having, for example, a specific
density which varies from 0.93 to 0.97 and a melt index
which can reach 20 lmeasured by the ASTM D 1238 method,
with a weight of 2.16 kg).
The catalytic system according to the present
invention is prepared by reacting the hydroxylated
aluminium support with a compound of a heavy metal of
Group IV to Group VI of the Periodic Table, and
subsequently activating the catalyst component thus formed
by treating it with an organic metal compound of a metal
of Group I to Group III of the Periodic Table.
Heavy metal compounds which are shown to be
par~icularly suitable are halides, oxyhalides and
alkoxyhalides.
Preferred heavy metals are titanium, vanadium and
chromium.
Suitable compounds are, therefore: TiC14, TiBr4,
VCl4, VOC13, V0Br3, CrO2C12, Ti(O_c2H5)3cl
and Ti(O-isoC4Hg)2Cl2. However, best results are
obtained with TiC14.
The conditions required for the reaction between the
hydroxylated aluminium support and the heavy metal
compound are not critical, and they may vary over a wide
range. The reaction temperature may vary from 0 to
300C, and the duration of the reaction from l to 4
hours. The heavy metal compound may be used in its pure
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state or in mixture with an anhydrous organic solvent.
It is pxeferable to use an excess of heavy metal
compound with respect to the hydroxylated aluminium
support.
Examples of organic metal compounds which may be used
include: metal alkyls, halides or hydrides of metal
alkyls; and Grignard compounds.
Examples of the relative metals are: aluminium; Zn;
Mg; Na; and Li. Thus, examples of suitable compounds are:
trimethylaluminium; monochlorodiethylaluminium; aluminium
diisobutylhydride; (C2H5)MgBr; and
ethylaluminiumsesquichloride.
However, best results are generally obtained with
aluminium alkyls or halides of alkyl aluminium. In
particular triethylaluminium and triisobutylaluminium are
excellent.
The quantity of organic metal compound to be used is
not critical. Preferably however, the compound should be
present in molar excess with respect to the heavy metal
contained in the support.
The catalytic system according to the present
invention is applicable to homo or copolymerisation of
~-olefines r for example ethylene, propylene, butene.1,
pentene.l, he~ene.l and 4-methyl-pentane.l.
It is particularly advantageous when used for the
preparation of homo or copolymers of ethylene. The homo
or copolymerisation of olefines may be carried out by any
of the usual methods, either in the gaseous phase or in
solution. In this second case, inert solvents are used,
for example, aliphatic or cyclo-aliphatic hydrocarbons.
The average molecular weight of the polymer to be
\, ,~ . . .
obtained may be controlled either b~ the choice of the
hydroxylated support, prepared in accordance with the
invention, or by the addition of one or more molecular
weight regulators, such as hydrogen, alcohols, CO2, Zn
alkyls or Cd alkyls.
The density of the product polymers may be controlled
by adding to the polymerisation reaction mixture an
alkoxide of a ~etal from Group IV or V of the Periodic
Table. Alkoxides of titanium or vanadium, for example Ti
(i-butoxy)4 are preferred.
As the melt index of the homo and coplymers obtained
by the present invention can vary over a very wide range,
these polymers are suitable for many types of operation,
such as extrusion or blow moulding.
Some examples are given hereinafter for purposes of
illustration. In no case are they to be considered as
limiting the invention. All melt index measurements were
made in accordance with the ASTM D 1238 method, with a
weight of 2.16 Kg.
COMPARATIVE EXAMPLE 1
5 g of ~-rhombic AlF3 are treated with 75 cc of pure
li~uid TiC14 and heated under reflux and strong
a~itation for one hour at a temperature of 136C. The
solid reaction product is separated, washed firstly with
TiC14 and then ~ith anhydrous n-heptane until free
chloride has completely disappeared from the wash
solvent. It is then dried.
The catalyst component thus prepared has a titanium
content of 1.5% by weight with respect to the support.
Polymerisation is then carried out in the following
manner:
0.2 g of the catalyst component are added to a
solution of l g of triethylaluminium in 1500 cc of
anhydrous n-heptane. The entire mlxture is then
transferred under anhydrous nitrogen into a 51.steel
autoclave provided with a bladed stirrer having a stirring
speed variable from 500 to 2000 r.p.m. The autoclave is
heated to a temperature of 90C and kept at this
temperature during polymerisation (l hour).
The pressure is raised to 4 Kg/cm2 with hydrogen and
then to 14 Kg/cm with ethylene. During polymerisationr
the partial pressure of the ethylene is kept constant by
continuously adding new ethylene. After one hour the
autoclave is degassed and the product discharged. The
yield is 180 g of polyethylene/g catalyst/h/atmosphere of
ethylene.
The specific activity of the catalyst component in
terms of the quantity of titanium contained in it is 12.0
kg of polyethylene/g Ti/h/atmosphere of ethylene.
The polymer has a melt index of 0.00 y/lO minutes.
E~AMPI,E l
5 g of ~-rhombic AlF3 are treated in a fluidised bed
with nitrogen saturated with lNl aqueous ammonia at a
temperature of 200C for 4 hours.
The compound thus obtained is treated with TiC14 to
prepare the catalyst component, using the same method as
~escribed in comparative example l. The catalyst
component thus prepared has a titanium content of 1. 8% by
weight with respect to the support.
Polymerisation is carried out as described in
comparative example l.
The yield is 610 g of polyethylene/g
catalyst/h/atmosphere of ethylene.
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,.
The specific activity of the catalyst component is
33.88 kg of polyethylene/g Ti/h/atmosphere of ethylene.
The polymer has a melt index of 4.0 g/10 minutes.
COMPARATIVE EXAMPLE 2
5 g of ~-hexagonal AlF3 are treated with TiC14 to
prepare the catalyst component using the same method as
described in comparative example 1. The catalyst
component thus prepared has a titanium content of 0.45% by
weight with respect to the support.
Polymerisation is carried out as described in
comparative example 1.
The yield is 67 g of polyethylene/g
catalyst/h/atmosphere of ethylene.
The specific activity of the catalyst component is
14.88 kg of polyethylene/g Ti/h/atmosphere of e-thylene.
The polymer has a melt index of 0.1 g/10 minutes.
EXAMPLE 2
5 g of ~-hexagonal AlF3 are treated in a fluidised
bed with helium saturated with water, at a temperature of
500C for 4 hours.
The compound thus obtained is treated with TiCl~ to
prepare the catalyst component, using the same method as
described in comparative example 1. The catalyst
component thus prepared has a titanium content of 0.65~ by
weight with respect to the support.
Polymerisation is carried out as described in
comparative example 1.
The yield is 193 g of polyethylene/g
catalyst/h/atmosphere of ethylene.
The specific activity of the catalyst component is
29.7 kg of polyethylene/g Ti/h/atmosphere of ethylene.
~r
The polymer has a melt index of 2.6 g/10 minutes.
EXAMPLE 3
5 g of ~-hexagonal AlF3 are treated in a fluidised
bed with helium saturated with water, at a temperature of
300C for 4 hours.
The compound thus obtained ls treated with TiC14 to
prepare the catalyst component, using the same method as
described in comparative example 1. The catalyst
component thus prepared shows a titanium content of 0.9%
by weight with respect to the support.
Polymerisation is carried out as described in
comparative example 1, except that instead of using
aluminium triethyl, an equal quantity (1 g) of aluminium
triisobutyl is used.
The yield is 315 g of polyethylene/g
catalyst/h/atmosphere of ethylene.
The specific activity of the catalyst component is
35.0 kg of polyethylene/g Ti/h/atmosphere of ethylene.
The polymer has a melt index of 1~5 9/10 minutes.
EXAMPLE 4
5 9 of ~-hexagonal AlF3 are treated in a fluidised
bed with nitrogen saturated with an aqueous solution
containing 3 g equivalent/litre of NH40H, at a
temperature o 200C for 4 hours.
The compound thus obtained is treated with TiC14 to
prepare the catalyst component, using the same method as
described in comparative example 1. The catalyst thus
prepared has a titanium content of 2.5~ by weight with
respect to the support.
Polymerisation is carried out as described in
comparative example 1.
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The yield is 750 g of polyethylene/g
catalyst/h/atmosphere of ethylene.
The specific activity of the catalyst component is
28,6 kg of polyethylene/g Ti/h/atmosphere of ethylene.
The polymer has a melt index of 2.0 g/10 minutes.
COMPARATIVE EXAMPLE 5
5 g of ~-hexagonal A1~3 are treated with 75 cc of
pure liquid VOC13 and refluxed at a temperature of 127C
for one hour with strong agitation. This solid reaction
product is separated, washed firstly with VOC13 and then
with anhydrous n-heptane until free chloride in the wash
solvent completely disappears. It is then dried.
The catalyst component thus prepared has a vanadium
content of 1.3~ by weight with respect to the support.
Polymerisation is carried out as described in
comparative example 1.
The yield is 210 g of polyethylene/g
catalyst/h/atmosphere o~ ethylene.
The specific activity of the catalyst component is
16.15 kg of polyethylene/g vanadium/h/atmosphere of
ethylene.
The polymer has a melt index of 0.2 g/10 minutes.
EXAMPLE 5
5 g of ~-hexagonal AlF3 are treated in a fluidised
bed with helium saturated with water, at a temperature of
300C for 4 hours.
The compound thus obtained is treated with VOC13 to
prepare the catalyst component, using the same me-thod as
described in comparative example 5. The catalyst
component thus prepared has a vanadium content of 2.7% by
weight with respect to the support.
- 10 -
,,
Polymerisation is carried out as described in
comparative example 1.
The yield is 760 9 of polyethylene/g
catalyst/h/atmosphere of ethylene.
The specific activity of the catalyst component is
28.1 kg of polyethylene/g vanadium/h/atmosphere of
ethylene.
The polymer has a melt index of 1.4 9/lO minutes.
EXAMPLE 6
5 g of A12~SO4)3 are treated in a fluidised bed
with nitrogen containing water vapour, at a temperature of
200C for 6 hours.
The compound thus obtained is treated with TiC14 to
prepare the catalyst component r using the same method as
described in comparative example 1. The catalyst
component thus prepared has a titanium content of 0.55~ by
weight with respect to the support.
Polymerisation is carried out as described in
comparative example 1,
The yield is 139 9 of polyethylene/g
catalyst/h/atmosphere of ethylene.
The specific activity of the catalyst component is
25.3 kg of polyethylene/g Ti/h/atmosphere of ethylene.
The polymer has a melt index of 0.5 9/10 minutes.
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