Note: Descriptions are shown in the official language in which they were submitted.
Case: 5023
li~;f~214
POLYMERISATION CATALYST .
The present invention relates to a supported '.iegler catalyst
for polymerising l-olefins and to a process for polymerising 1-
olefins employing the catalyst.
It has long been known that l-olefins such as ethylene can be
S polymerised by contacting them under polymerisation conditions with
a catalyst obtained by activating a transition metal-containing
component, e.g. a titanium compound such as titanium tetrachloride,
with an activator or co-catalyst, e.g. an organo-metallic compound
such as triethylaluminium. Catalysts comprising the transition
metal-containing component and the co-catalyst or activator are
generally referred to in the art as "Ziegler catalysts" and this
terminology will be used throughout this specification.
The Ziegler catalyst component comprising the transition metal
can be used either in an unsupported condition, or supported on
support materials such as silicon carbide, calcium phosphate,
silica, magnesium carbonate or sodium carbonate.
UK Patent Specification No: 1 256 851 discloses a catalyst
for the low-pressure polymerisation and copolymerisation of
olefins, comprising:
(a) an organometallic compound, or an organosilicon compound
having at least one Si-H bond, and
(b) a solid product obtained by reacting a substantially
anhydrous support consisting of a solid bivalent-metal
compound with an organometallic compound, or an organo-
silicon compound having at least one Si-H bond, this being
either identical to or different from "(a)", separating the
solid product resulting from the reaction, reacting this
product with a halogenated derivative of a transition metal,
~'~
i4
and separating the final solid reaction product; the
molar ratio of "(a)" to the transition metal chemically
bonded to the support being at least 2.
UK Patent Specification 1 306 044 relates inter alia to a
process for polymerising alpha-olefins using a catalyst comprising
an organometallic compound and the solid product obtained by reacting
silica or alumina with an excess of a compound of the formula MR Xm
wherein M is aluminium or magnesium, R is a hydrocarbon radical, x is
hydrogen or halogen, m is the valency of M and n is a whole number
not greater than m, separating and washing the solid product and
reacting it with an excess of a halogen-containing transition
metal compound and separating the solid reaction product.
UK Patent Specificatlon 1 351 488 discloses a catalyst
composition, for polymerising l-olefins, comprising (A) a component
prepared in an inert atmosphere by
(a) treating a mixture of a hydrocarbon solvent and, as carrier,
a finely divided solid calcium or magnesium inorganic
compound other than calcium carbona e which compound does
not contain halogen and which is substantially insolu;~le in
the hydrocarbon solvent, with 0.05 to 10 millimols, per
gram of the calcium magnesium compound, of an organo-
aluminium compound,
~b) treating the product of (a) with a vanadium halide or
with a mixture of a vanadium halide and a titanium
halide containing not more than 5 mols, per mol of vanadium
halide, of ti*anium halide; the total mols of vanadium
or of vanadium and titanium added being 0.001 to 1 mol/mol
of organo groups in the organoaluminium compound; and
~c) allowing the ingredients to react and, if necessary
removing unreacted vanadium and/or titanium halide to
provide a reaction product which is substantially free
from unreacted vanadium and titanium halide; and
: ~B) an organoaluminium compound.
It is an object of the present invention to provide an improved
supported Ziegler catalyst.
14
Accordingly the present invention provides a supported Ziegler
catalyst prepared by the following steps, carried out under anhydrous
conditions:
(A) reacting a hydroxyl groups-containing support material
comprising magnesium silicate or silica and magnesia
with one or more organometallic compounds having the
general formula M~ a Qb a wherein M is a metal which is
aluminium, boron, lithium, zinc or magnesium~
R is a hydrocarbyl group, Q is halogen or an oxyhydrocarbyl
group, b is the valency of M and a is an integer from
1 to b,
(B) removing unreacted organometallic compound, if any, from the
produced solid material,
(C) impregnating the solid material obtained from step B with one
or more halogen-containing transition metal compounds wherein
the transition metal(s) comprise titanium, vanadium or
zirconium.
Throughout this specification, boron is regarded as a metal. The
support material employed in step A in the preparation of the catalyst
~f the present invention is preferably an intimate mixture of silica
and magnesia or a coprecipitate of silica and magnesia. The preparation
of coprecipitated silica-magnesia is well known in the art.
Coprecipitates of silica and magnesia are commercially available.
Intimate mixtures of silica and magnesia can be prepared, for example
by ball milling a mixture of the two oxides. A further method of
forming a support material comprising silica and magnesia suitable
for use in the present invention comprises heating a mixture of a
particulate silica support material and a magnesium ccmpound which
decomposes at least partially into magnesia on heating. Examples
of magnesium compounds which can be suitably heated with silica in
this manner are magnesium alkoxides, e.g. magnesium ethoxide,
magnesium alkyls, e.g. dibutyl magnesium, magnesium hydroxide,
magnesium carbonate and magnesium nitrate. In the present invention
it is preferred to use a coprecipitated silica-magnesia as the support
material.
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The atomic ratio of silicon : magnesium in the support
material employed in the present in~ention is suitably in the
range 100:1 to 1:100, preferably 20:1 to 1:20.
The support material should be substantially dry before
reacting with the organometallic compound and is preferably dried
by heating for several hours in a vacuum oven at a temperature
in the range 70 to 150C. Heating overnight in vacuo at about
150C normally gives adequate drying.
The organometallic compound used to prepare the catalyst of
the present invention must contain at least one metal-carbon bond.
Preferred organometallic compounds are trihydrocarbyl aluminium,
trihydrocarbyl boron, dihydrocarbyl zinc or magnesium and hydrocarbyl
lithium compounds. Examples of organometallic compounds which
can be employed are triethyl aluminium, isoprenyl aluminium, diethyl
aluminium chloride, diethyl aluminium ethoxide, triethyl boron,
dibutyl magnesium, ethyl magnesium bormide, diethyl zinc and butyl
lithium. Aluminium trialkyls are particularly preferred, especially
those containing 1 to 10 carbon atoms in each alkyl group.
The quantity of organometallic compound employed in step A is
suitably in the range 0.1 to 10 moles, preferably O.S to 1.5 moles
per mole of surface hydroxyl groups on the support material.
The reaction between the organometallic compound and the
support material can be conducted in any desired manner provided
that the reaction mixture is substantially free from water and
other materials containing reactive groups which react with the
organometallic compound. The reaction can be conducted in the
presence of an inert diluent or solvent for the organometallic
compound if desired. Examples of suitable solvents are liquid
hydrocarbons, for example, cyclohexane or normal-hexane. The
reaction is preferably carried out in a solvent at a temperature
between ambient and the boiling point of the solvent, for example at a
temperature in the range 10-80~ although temperatures above or
below this range can be employed if desired. The reaction between
the organometallic compound and the support material generally
occurs rapidly at ambient temperature and a reaction time of one
.214
hour or less is normally adequate although longer times can be
employed if desired.
After the reaction between the organometallic compound and
the support material is substantially complete, the unreacted
(i.e. unadsorbed) organometallic compound, if any, is separated
in step B from the solid product from step A. The separation is
preferably achieved by washing the solid product with an anhydrous
inert solvent, for example, cyclohexane, normal-hexane or petroleum `
ether. The solid product must be protected from contact with other
substances with which it may deleteriously react, or example
air.
In step C the solid product is impregnated with one or more
halogen-containing titanium compounds and/or one or more halogen-
containing vanadium compounds and/or one or more halogen-containins
zirconium compounds wherein the titanium is preferably tetravalent,
the vanadium is preferably tetra- or penta-valent and the zirconium
is preferably tetravalent. Preferably these compounds are selected
from compounds having the general formulae DX , DOX( 2) and D(OR2)
Xm n wherein D is the titanium, vanadium or zirconium; X is halogen,
preferably chlorine; 0 is oxygen; R is a hydrocarbyl group, for
example alkyl, aryl or cycloalkyl, preferably containing 1-10 carbon
atoms; m is the valency of D; and n is an integer from 1 to m-l.
Examples of suitable titanium compounds are titanium tetrachloride,
trichloro-titanium ethylate, dichlorotitanium diisopropylate and
titaniumoxychloride. Examples of suitable vanadium compounds are
vanadyl chloride and vanadium tetrachloride. Examples of suitable
zirconium compounds are zirconium tetrachloride and zirconyl chloride.
Titanium tetrachloride and vanadyl chloride are preferred.
The quantity of transition metal compound employed in preparing
the catalyst of the present invention is suitably 0.1 to lO moles,
preferably 0.25 to l.S moles, most preferably 0.4 to 1.0 moles per
mole of organometallic compound residue bound to the support surface.
The quantity of organometallic compound residue bound to the support
surface can conveniently be determined by conventional analytical
techniques, for example, elementary analysis. When it is desired
14
to use titanium and vanadium compounds preferably the atomic ratio
of Ti:V is in the range 100:1 to 1:100 most preferably 5:1 to 1:5.
When more than one transition metal compound is employed, the
impregnation step C can be carried out by impregnating the solid
product from step B with the transition metal compounds separately
or together. It is preferred to impregnate using a mixture of the
titanium and vanadium compounds. The impregnation can be carried
out using the neat (undiluted) transition metal compound or by
dissolving one or more of them in an inert solvent for example a
liquid hydrocarbon solvent. The inert solvent, when used, must be
free from functional groups capable ~f reacting with the solid
material obtained from step B and the transition metal compound.
Cyclohexane is an example of a suitable inert solvent. The
impregnation step is preferably carried out by contacting the solid
material obtained from step B with the transition metal compound at
a temperature in the range 10 to ~50C. It is particularly preferred
to carry out the impregnation by stirring the mixture of said solid
material and transition metal compound in an inert solvent at a
temperature in the range 10 to 30C. The contacting in the impregnation
step C is preferably carried oùt for a time in the range 10 minutes to
24 hours.
Preferably, the catalyst obtained from step C is separated from
any unadsorbed transition metal compound by conventional means,
for example, washing with dry inert solvent, or, if a volatile
transition metal compound has been employed, by purging with inert
gas, e.g. nitrogen, helium or argon. Preferably the separation is
carried out by washing the catalyst component several times with
aliquots of dry hydrocarbon solvent. The catalyst may be stored as
the dry material in a suitable non-reactive atmosphere, e.g. argon,
nitrogen or other inert gas, or as a slurry in inert solvent.
The present invention further comprises a process for poly-
merising one or more 1-olefins comprising contacting the monomer
under polymerisation conditions with the catalyst component of the
present invention preferably in the presence of a Ziegler catalyst
activator. Ziegler catalyst activators and the methods is which
~i~c;8214
they are used to activate Ziegler catalysts are well ~nown.
Ziegler catalyst ~ctivators are organometallic derivatives or
hydrides of metals of Groups I, II, III, and IV of the Periodic
Table. Particularly preferred are trialkyl aluminium compounds or
alkylaluminium halides, for example triethylaluminium, tributyl-
aluminium and diethylaluminium chloride. When a Ziegler catalyst
activator is employed, preferably it is present in an amount such
that the ~omic ratio of metal atoms in the activator : total
transition metal supported on the catalyst support is not greater
than 10:1.
The polymerisation process of the present invention can be
applied to the homopolymerisation of l-olefins, e.g. ethylene or
propylene, or to the copolymerisation of mixtures of 1-olefins,
e.g. ethylene with propylene, l-butene, l-pentene, l-hexane, 4-
methylpentene-l, 1,3-butadiene or isoprene. The process is
particularly suitable for the homopolymerisation of ethylene or
the copolymerisation of ethylene with up to 40% weight (based on
total monomer) of comonomers.
The polymerisation conditions can be in accordance with knowr.
techniques used in supported Ziegler polymerisation. The poly-
merisation can be carried out in thé gaseous phase or in the presence
of a dispersion medium in which the monomer is soluble. As a liquid
dispersion medium, use can be made of an inert hydrocarbon which is
liquid under the polymerisation conditions, or of the monomer or
monomers themselves maintained in the liquid state under their
saturation pressure. The polymerisation can if desired be carried
- out in the presence of hydrogen gas or other chain trans~er agent to
vary the molecular weight of the produced polymer.
The polymerisation is preferably carried out under conditions
such that the polymer is formed as solid particles suspended in
a liquid diluent. Generally the diluent is selected from paraffins
and cycloparaffins having from 3-30 carbon atoms per molecule.
Suitable diluents include for example isopentane, isobutane, and
cyclohexane. Isobutane is preferred.
Methods of recovering the product polyolefin are well known
Z14
in the art.
The polymerisation catalyst of the present invention can be
used to make high density ethylene polymers and copolymers at
high productivity having properties which render them suitable
for a variety of applications. By varying the amounts of transition
metal compounds and/or organometallic compound used in steps
A and C of the catalyst preparation, control can be exercised over
the molecular weight distribution of polyolefins prepared over
the catalyst.
The invention is further illustrated by the following
Examples and Comparative Test.
The melt index (MI2 16) and high load melt index
(MI21 6) were determined according to AS~M method 1238
using 2.16 kg and 21.6 kg loads repsectively; the units are grams
per 10 minutes. Kd is determined by a method similar to that
disclosed in Sab~a~ R., J. Appl. Polymer Sci. 1963,7, 437.
Examples 1 & 2 - CatalYst Pre~aratlon
.
The following procedure was used for the preparation of the
catalysts. The quantities of the reagents used and analyses of the
driéd catalysts are shown in Table 1.
In step A silica-magnesia (Davison Grade 300) was dried overnight
under vacuum at 150C. 10 g of the dried material was suspended in
dry cyclohexane (150 ml) in a vessel purged with dry nitrogen and a
10% w/w solution of triethylaluminium in hexane added dropwise, with
stirring. The suspension was stirred for 90 min after the addition
was complete, and then allowed to settle. The supernatant liquor
was decanted off, (step B), and 150 ml of fresh dry cyclohexane added.
In step C, a mixture of titanium tetrachloride and vanadium oxytri-
chloride dissolved in dry cyclohexane (60 ml) was added dropwise, with
stirring, to the reaction vessel. Stirring was continued for 90 min
after the addition was complete. The catalyst was washed with
cyclohexane (180 ml) and the volume made up to ca. 350 ml with
fresh dry cyclohexane. The catalyst was used as a slurry and stored
.~
214
under nitrogen.
PolYmerisation
Polymerisation was carried out in a 2.3 litre capacity
stainless steel stirred autoclave. The reactor was purged with
S dry nitrogen, baked for 2 hours at 110C and then cooled to
75C. The catalyst slurry was added to the reactor using
a syringe. Triethyl aluminium (0.5 ml of a 10% weight/weight
solution of AlEt3 in hexane) was added to improve the catalyst
activity, together with isobutane (1 litre). The vessel was
reheated to 90C and hydrogen (6.9 bar) was introduced. Then
ethylene was introduced to bring the total pressure in the
reactor to 41.4 bar, and further ethylene was introduced throughout
the duration of the polymerisation to maintain the pressure at
41.4 bar. The polymerisation temperature was 90C.
lS At the end of the polymerisation (1 hour) the diluent
and unreacted ethylene were vented off and the polyethylene powder
recovered. The polyethylene was washed with acetone and treated
with conventional stabilizer and the-properties (see Table 2)
measured using standard procedures. It can be seen from Examples
1 and 2 that the catalyst according to the present invention
polymerises ethylene at high activity to give polymer having a
fairly broad molecular weight distribution (MWD). In both Examples,
a catalyst containing both titanium and vanadium was employed and
it can be seen that the catalyst having the lower Ti:V ratio gave
polymer having broader MWD (high ~d is indicative of broad MWD).
Comparative Test; Catalyst PreParation
The catalyst was prepared in the same manner as the catalysts
in Examples 1 and 2, except that silica (Davison 951 Grade) was
used in place of silica magnesia. The quantities of reagents used
- 30 were as in Example 1 (ie lOg support material, 3.9g AlEt3, 0.35g
TiCl and 1.25g VOC13). Analysis of the dried catalyst showed it
to contain 6~2% Al~ 0.84% Ti~ 2.5% V and 6.6% Cl.
PolYmerisation
Polymerisation was carried out using the procedure described
for E~amples 1 and 2. Using 124 mg of catalyst, only 6~3g of polymer
were produced after lh~ corresponding to an activity of 550 kg/kg/h.
The polymer produced has MI2 16 = 0.58g/10 mln, MI21 6 = 33.2g/10 mln
and Kd = 7.4.
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