Note: Descriptions are shown in the official language in which they were submitted.
50~2
Z13
POLYMERISATION CATALYST
The present invention relates to a supported Ziegler catalyst
for polymerising l-olefins and to a process for polymerising l-olefins
employing the catalyst.
It has long been known that l-olefins such as ethylene can be
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
3uch as triethylaluminium. Catalysts comprising the transition metal-
10 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
15 support materials such as silicon carbide, calcium phosphatej silica,
magnesium carbonate `and 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 organosilicon compound
25 having at least one Si-H bond, this being either identical to or
'
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different from "(a)", separating the solid product resulting from the
reaction, reacting this pcoduct with a halogenated derivative of a
transition metal, 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 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 MRnX 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.
It is an object of the present invention to provide an improved
supported Ziegler catalyst.
Accordingly the present invention provides a supported Ziegler
catalyst prepared by the following steps:
(A) heating together at a te~,perature in the range 250 to 1100 C
a refractory oxide support material having surface hydroxyl groups and
one or more halogen-free metal derivatives which are hydrides and~or
organic derivatives of the metal,
(B) ~eacting the product from step ~A) with one or more
organometallic compounds having the general formula MR a Q b a wherein
M is the a metal atom~ Rl 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 and wherein the metal is aluminium, boron, lithium, zinc or
magnesium,
(C) impregnating the solid product from step (B) with one or more
halogen-con~aining transition metal compounds wherein the transition
metal or metals comprise titanium and/or vanadium, and/or zirconium.
Throughoutthis specification silicon and boron are regarded
as metals.
In step A the refractory oxide support material is suitably any
2:13
particulate oxide or mixed oxide, e.g. silica, silica-alumina, alumina,
zirconia, thoria, titania or magnesia, having surface hydroxyl groups
capable of reacting with the halogen free metal derivative
Preferred support materials are those suitable for use in the
S well known Phillips process for the polymerisation of ethylene
(see for example UK Patent Specifications 790, 195; 804,641;
853,414; French Patent Nos. 2,015,128; 1,015,130 and Belgian
Patent No. 741,437). Microspheroidal silicas and silica-aluminas
having a mean particle diameter in the range 30 to 300 ~m, a surfaee
10 area of 50 to 1000 square metres per gram and a pore volume of 0.5
to 3.5 cc/gram are particularly preferred.
The metal in the halogen-free metal derivative is suitably
selected from titanium, al~minium, nickel, vanadium, zirconium,
boron~ magnesium, silicon, zinc or tin.
me halogen-free metal derivative contains one or more hydride
"atoms" and/or one or more organic groups. By an organic group is
meant a group containing at least carbon and hydrogen, optionally
concaining oxygen and/or nitrogen. Examples of suitable organic
groups are alkyl, aryl, alkenyl, alkoxy, aryloxy, carboxylate or alkyl-
20 amino. The organic group can be mono- or poly-valent. ~xamples
of halogen-free metal derivatives are titanium tetraisopropylate~
titaniùm acetylacetonate~ titanocéne diacetate~ triethylaluminium~
diethylalul~inium hydride~ dibutylaluminium hydride~ aluminium
isopropylate~ nickel acetate~ nickél acetylacetonate, nickelocene
25 vanadylethylate (VOEt3), vanadyl isopropylate, zircc~nium tetraiso-
propylate, zirconium tetrabutylate, triethyl boron, triethyl borate,
magnesium diethylate, dibutyl magnesium, tetraethyl silicate,
diethyl zinc, tributyl tin hydride and butyl octyl magnesium.
me c~uantity of halogen-free metal derivative employed in step
30 (A) of the present invention is suitably 0.005 to 2.0 moles, preferably
0.1 to 0.5 moles based on the number of moles of hydroxyl groups
present in the refractory oxide support material.
If the halogen-free metal derivative reacts with water, it is
preferred to dry the refractory oxide support material prior to the
35 performance of step (A) of the present invention and to carry out
step (A) under substantially anhydrous conditions.
213
The refractory oxide support material and the halogen-free
metal derivative are brought together in step A of the present
invention in any desired manner. If the halogen-free metal derivative
is a solid it is preferred to dissolve the solid in a suitable inert
liquid diluent and to mix the solution with the refractory oxide
and evaporate the diluent prior to or during the heating in step A.
The heating in step A is carried ~ut at a temperature in the range
250 to 1100C, preferably 400 to 900C. The heating may be continu~d
as long as desired but is preferably carried out for a length o~ tim-
within the range 30 minutes to 24 hours. The heating may be carri~dout, for example, in vacuo, in an inert gas atmosphere (e.g. nitrogen
or argon), or in air. Preferably the mixture of refractory oxide
support material and halogen-free metal derivative are fluidised
by inert gas or air during the heating in step A.
The product from step A in the present invention is then reacted
with the organometallic compound defined in step B. The organo-
metallic compound must contain at least one metal-carbon bond.
Preferred organometallic compounds are trihydrocarbyl aluminium, tri-
hydrocarbyl boron, dihydrocarbyl zinc or magnesium and hydrocarbvl
lithium c~mpounds. 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 bromide, diethyl zinc and butyl lithium. Aluminium tri-
alkyls are particularly preferred, especially those containing 1 to
10 carbon atoms in each alkyl group.
The quantity of organometallic compound employed in step B is
suitably in the range 0.1 to 10.0 moles, preferably 0.5 to 1.5 moles
per mole of surface hydroxyl groups on the original refactory oxide
support material.
3~ The reaction between the organometallic compound and the product
from step A can be conducted in any desired manner provided that the
reaction mixture is substantially free from water and other impurities
containing reactive groups which react with the organometallic compound.
The reaction can be conducted in the present 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 10-80C~
although temperatures above or below this range can be employed if
desired. The reaction between the organometallic compound and the
product from step A generally occurs rapidly at ambient temperature
and a reaction time of one hour or less is normally adequate although
longer times can be employed if desired.
After the reaction between the organometallic compound and the
product from step A is substantially complete, the unadsorbed
organometallic compound, if any, can be separated from the solid
product from step B if desired. The separation can be acnieved, for
example, 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 ~ith ~hich
it may deleteriously react, for example air.
In step C the solid product is impregnated with one or more
halogen-containing transition metal compounds wherein the transition
metal or metals comprise titanium, vanadium or zirconium.
The titanium or zirconium is preferably tetravalent and the vanadium
is preferably tetra- or penta-valent. Preferably these compounds are
selected from compounds having the general formulae DY, DOY( 2) and
D(OR )sY wherein D is the titanium, vanadium or zirconium; Y is
halogen, preferably chlorine; 0 is oxygen; R is a hydrocarbyl group,
for example alkyl, aryl or cycloalkyl preferably containing 1-10 carbon
atoms; p is the valency of D; and s is an integer from 1 to p-l.
Examples of suitable titanium compounds are titanium tetrachloride t
trichlorotitanium ethylate, dichlorotitanium diisopropylate and
titanium oxychloride. 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 or mixtures thereof are
preferred.
The quantity of transition metal compound employed in preparing
Z13
the catalyst of the present invention is suitably 0.05 to 10 moles,
preferably 0.1 to 1.5 moles, most preferably 0.4 to l.0 moles ?er
mole of hydroxyl groups in the original support material. When a
mixture of titanium and vanadium compounds is employed in step C of the
present invention, preferably the atomic ratio of Ti:V used in the
catalyst preparation is in the range 100:1 to 1:100, most preferably
10:1 to 1:10~
The impregnation can be carried out using the neat (undiluted)
transition metal compounds or by dissolving the transition metal
compound(s) in an inert solvent, for example a liquid hydrocarbon
solvent. The inert solvent when used must be free from functional
groups capable of reacting with the solid material obtained from step
B and the transition metal compound(s). 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(s) 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(s) in
an inert solvent at a temperature in the range 10 to 30C. The
contacting in the impregnation step C is preferably carried out for a
time in the range 10 minutes to 24 hours.
The catalyst obtained from step C is preferably separated from any
un~bsorbed transition metal compound by conventional means, for example,
washing with dry inert solvent, or, if volatile transition metal
compound(s) have been employed, by purging with inert gas, e.g. nitrogen,
helium or argon. Preferably the separation is carried out by washing
the catalyst 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 polymerisingone or more l-olefins comprising contacting the monomer under poly-
merisation conditions with the catalyst of the present invention,
preferably in the presence of a Ziegler catalyst activator. Ziegler
catalyst activators and the methods in which they are used to
13
activctte ~iegler cataly ts are well know~ iegler catalyst
ac~ivators are organome~clllic deriv.ltives or hydrides of metals of
Grolll>s ~.~ Il, LlI, ~ d l`V o1 ~ e ~ riodic Tal~l~ . P~lt-ti~-ularly
preferre~ re trialkyl alumirlium ~ompouTIds or alkylalumlrlium
halides, for example triethylaluminium, tributylaluminium and
diethy~aluminium chloride. When a Ziegler catalyst activator
is employed, preferably it is present in an amount such that
the atomic 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 l-olefins,
e.g. ethylene with propylene, l-butene, l-pentene, l-hexene,
4-methylpentene-1, 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 witn knowl-
techniques used in supported Ziegler polymerisation. The poly-
merisation can be carried out in the 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 transfer 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 irl
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 preférred.
Methods of recovering the product polyolefin are well known
in the art.
li~il~213
The polymerisation catalys~ of the preserlt invention can
be used to make high density etllylene polymers and copolymers
at high productivity having properties which render them s~table
for a variety of applications. The catalyst exhibits good hydrogen
sensitivity, i.e. the melt index of the produced polyolefins can
be varied widely by employing hydrogen at different concentrations
as chain transfer agent in the polymerisation process.
The invention is further illustrated by the following ~xamples.
In the Examples the melt index (MI2 16) and high load melt
index (MI21 6) were determined according to ASTM method D 1238
conditions E and F respectively; the units are grams per lO
minutes.
Kd is a numerical measure of the molecular weight distribution
of the polymer and is determined by a method similar to that
disclosed in Sabia, R., J. Appl. Polymer Sci., 1963, 7, 347.
Example 1
Catalyst Preparation
In step A of the catalyst preparation, silica
(Davison 951 grade, 359) was slurried in petroleum
ether (40-60C boiling range, 250 ml) in a nitrogen purged flask
and titanium tetraisopropylate (10.6 ml) added. Stirring was
continued for 1 hour after which the petroleum ether was removed on
- a rotary evaporator. The dried support was heated at 750C in a
bed fluidised with air for 5 hours. In step B, 10g of the resulLing
material, which contained 6.0% titanium by weight, were stirred in dry
cyclohexane (150 ml) in a nitrogen purged flask. Triethylaluminium
(10% w~w solution in hexane, 43 ml, 3.09) was added dropwise, with
stirring. Stirring was continued for 90 min after the addition was
complete. The suspension was allowed to settle, the supernatant
liquor decanted off, and fresh dry cyclohexane (150 ml) added. In step
C, a mixture of titanium tetrachloride (1.08g) and vanadium oxytri-
chloride (1.259) 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 allowed
to settle, the supernatant liquor decanted off, and the volume made
llt;~Zi3
up to ca. 350 ml with fresh dry cyclohexane. The catalyst was
used as a slurry and stored under nitrogen. A sample of the catalys-
was dried and found by elementary analysis to contain 3.4% Al,
5.4% Ti, 2.3% V and 9.5% Cl.
Polymerisation
Polymerisation was carried out in a 2.3 litre capacity
stainless steel stirred autoclave. The reactor was purged with
dry nitrogen, baked for 2 hours at 110C and then cooled to
75C. The catalyst slurry (118 mg dry weight) 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.
At the end of the polymerisation (about 1 hour) the diluent
and unreacted ethylene were vented of and the polyethylene powder
recovered. The polyethylene yield was 348g and the catalyst activity
2950 kg/kg/hour. The polyethylene was washed with acetone and
treated with conventional stabilizer and the properties measured
using standard procedures. The polymer properties were as follows
M12,16 was l.Og/10 minutes, M121 6 was 34.7 g/10 minutes, Kd was
2.4. Screening through standard sieves showed that the polymer
only contained 0.7 wt % of particles below 106 ~m.
Exam~le 2
Silica (Davison 952 Grade~ 40g) was suspended in a solution of
al~minium isopropoxide (l5.lg) in toluene (500ml) and the mixture
heated under reflux~ with stirring~ for 2~ hours. The solvent
was removed on a rotary evaporator and the dried powder calcined
for 2 hours at 500C in a bed fluidised with air. The support
- material was cooled in a flow of dry nitrogen and stored under
nitrogen prior to use. A portion of this material was used in the
remaining catalyst preparation steps (steps 'B' and 'C'); these
:, ,
lltiS~13
were carried out in the same manner as described in ~xample 1,
except that the catalyst was washed with cyclohexane (250ml)
before finally being made up with cyclohexane. The quantities
of the reagents used are shown in Table 1.
PolYmerisation
Polymerisation was carried out as described in Example 1.
Polymerisation results and polymer properties are summarised
in Table 2.
Example 3
Silica (Davison 952 Grade, 40g) was suspended in a solution
of nickel acetate (8.47g) in ethanol (300ml) and the mixture stirred
for 15 min. The solvent was removed on a rotary evaporator ~nd
the dried powder calcined for 1 hour at 550C in a bed fluidised
with air. The support material was cooled in a flow of dry nitrogen
and stored under nitrogen prior to use. Analysis of the support
material sh~ed it to contain 4.7% Ni by weight. A portion of this
material wa~ used in the remaining catalyst preparation steps
(steps 'Bl and 'C'); these were carried out in the same manner as
described in Example 1~ except that the alkylated support was
2C washed with cyclohexane ~250ml) after decantation (end of step 'B')
and the catalyst was washed twice with cyclohexane (250ml each time)
after decantation (end of step 'C'). The quantities of reagents
used and the analysis of the dried catalyst are shown in Table 1.
Pol~merisation
Polymerisation was carried out as described in Example 1.
Polymerisation results and polymer properties are summarised
in Table 2.
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