Preparation of supported catalyst using trialkylaluminum-metallocene contact products

The supported catalyst disclosed herein is a contact product of two components. One component is the contact product of silica containing hydroxyl groups and alumoxane. This second component is the paraffinic-hydrocarbon soluble contact product of a metallocene compound of a transition metal and a trialkylaluminum compound.

FIELD OF THE INVENTION 
The invention relates to new catalyst compositions. In particular, the 
invention relates to supported metallocene catalysts and new methods of 
their synthesis. 
BACKGROUND OF THE INVENTION 
Metallocene catalysts, activated by alumoxanes, were introduced to the art 
of catalysis in the late 1970s. The efforts to maximize their efficacy 
have led to various unique developments. Because of the initial problems 
involving alumoxanes, some of the developments involved different 
techniques for producing the cocatalyst (or activator) and to alternatives 
of activating metallocene complexes. 
SUMMARY OF THE INVENTION 
The invention relates to a supported (heterogeneous) catalyst. The catalyst 
takes the form of particles which are free flowing and comprise a fully 
activated, single-component metallocene catalyst. 
The supported catalyst is a contact product comprising components (A) and 
(B). Component (A) is the contact product of silica containing hydroxyl 
groups and alumoxane. The molar ratio of hydroxyl groups on the silica 
surface to aluminum provided by alumoxane ranges from 0.01 to 1.50. 
Component (B) is the contact product of a metallocene compound of 
transition metal and a trialkyaluminum compound; the contact product of 
(B) is soluble in a paraffinic hydrocarbon containing at least 5 carbon 
atoms. The transition metal compound has the formula Cp.sub.x 
M(R.sup.1).sub.y (R.sup.2).sub.2, wherein Cp is a cyclopentadienyl group, 
unsubstituted or substituted, x is 1 or 2; M is zirconium, hafnium, or 
titanium; each of R.sup.1 and R.sup.2 is selected from the group 
consisting of a halogen atom, a hydrogen atom, and an alkyl group, 
providing that x+y+z is equal to the valence of the M; the 
trialkylaluminum compound in the contact product (B) is characterized by 
the formula Al(R.sup.3).sub.a (R.sup.4).sub.b (R.sup.5).sub.c wherein each 
of R.sup.3, R.sup.4, and R.sup.5 is a straight-chain or branched alkyl 
group containing 1 to 10 carbon atoms, wherein R.sup.3, R.sup.4, and 
R.sup.5 are the same or different, and wherein the sum of a+b+c is equal 
to 3. The metallocene transition metal compound per se is not very soluble 
in said paraffinic hydrocarbon and the transition metal compound 
derivatives affixed to said support are not soluble in the paraffinic 
hydrocarbon. 
The invention also comprises a process for preparing a catalyst composition 
comprising providing silica which has been dehydrated at temperatures 
ranging from 200.degree. to 750.degree. C.; contacting said silica with an 
amount of alumoxane; impregnating the contact product with a solution of 
an intermediate which has been formed by contacting a metallocene compound 
of a transition metal with a trialkylaluminum compound in a paraffinic 
hydrocarbon which is a solvent for the intermediate and in which the 
transition metal compound itself is not very soluble,wherein the 
transition metal compound has the formula Cp.sub.x M(R.sup.y).sub.y 
(R.sup.2).sub.2 in which the Cp, x, M, R.sup.1, R.sup.2 x+y+z are defined 
as above; and recovering a supported catalyst in which M and derivatives 
thereof are fixed to the silica and are insoluble in said hydrocarbon. 
DETAILED DESCRIPTION OF THE INVENTION 
The catalyst of the invention is a supported (heterogeneous) catalyst and 
comprises 0.05 to 2.00 weight percent (wt. %), preferably 0.10 to 0.60 wt. 
% of a transition metal provided by a metallocene compound of a transition 
metal of the formula Cp.sub.x M(R.sup.1).sub.y (R.sup.2).sub.2. The 
catalyst comprises two sources of aluminum. It is characterized by a total 
aluminum content of 5 to 20 wt. %, preferably 8 to 15 wt. % of aluminum 
which refers to the total aluminum content provided by both a 
trialkylaluminum compound and an alumoxane. (The foregoing weight percents 
are based on the combined weight of support and metals). 
The catalyst comprises a contact product, and derivatives thereof, of an 
alumoxane and the support, silica or silica/alumina, or alumina. The 
catalyst composition of the invention can be characterized as the contact 
product of components (A) and (B), wherein: 
component (A) is the contact product of a support, such as silica 
containing hydroxyl groups, and an alumoxane; and, 
component (B) is the contact product of a metallocene compound of a 
transition metal and an alkylaluminum compound such as a trialkylaluminum 
compound. 
The support for the catalyst may be any carrier material which contains 
surface hydroxyl groups. 
The preferred carrier material for the catalyst is a solid, particulate, 
porous, inorganic material, such as an oxide of silicon and/or of 
aluminum. The carrier material is used in the form of a dry powder having 
an average particle size of from about 1 micron to about 500 microns. The 
surface area of the carrier is at least about 3 m.sup.2 /g, and preferably 
from at least 50 m.sup.2 /g up to 350 m.sup.2 /g. The carrier material 
should be dry, that is, free of absorbed water. Drying of the carrier 
material can be effected by heating at about 100.degree. C. to about 
1000.degree. C. When the carrier is silica, it is heated to at least 
200.degree. C., preferably about 200.degree. C. to about 850.degree. C., 
and most preferably at about 600.degree. C. The number of hydroxyl groups 
(silanol groups in the case of silica) is inversely proportional to the 
temperature of dehydration: the higher the temperature the lower the 
hydroxyl content. The carrier material must have at least some active 
hydroxyl (OH) groups on its surface to produce the catalyst composition of 
this invention. 
In the most preferred embodiment, the carrier is silica which, prior to the 
use thereof in the first catalyst synthesis step, has been dehydrated by 
fluidizing it with nitrogen and heating at about 600.degree. C. for about 
4-16 hours to achieve a surface hydroxyl group concentration of about 0.7 
millimoles per gram (mmol/g). The silica of the most preferred embodiment 
is a high surface area, amorphous silica (surface area=300 m.sup.2 /g; 
pore volume of 1.65 cm.sup.3 /g), and it is a material marketed under the 
tradenames of Davison 952 or Davison 955 by the Davison Chemical Division 
of W. R. Grace and Company or Crosfield ES70 by Crosfield Limited. The 
silica is in the form of spherical particles, which are obtained by a 
spray-drying process. As procured, these silicas are not calcined and thus 
must be dehydrated as indicated above. 
Alumoxane is a class of oligomers which includes methylalumoxane. 
Methylalumoxane (MAO) is used as a cocatalyst with metallocene catalysts. 
The class of alumoxanes comprises oligomeric linear and/or cyclic 
alkylalumoxanes represented by the formula: R--(Al(R)--O).sub.n 
--AlR.sub.2 for oligomeric, linear alumoxanes and (--Al(R)--)O--).sub.m 
for oligomeric cyclic alumoxanes wherein n is 1-40, preferably 10-20, m is 
3-40, preferably 3-20 and R is a C.sub.1 -C.sub.8 alkyl group or mixtures 
thereof, preferably a methyl group. MAO is a mixture of oligomers with a 
very wide distribution of molecular weights and usually with an average 
molecular weight of about 1200. MAO is commonly produced by reacting 
trimethylaluminum with water or with hydrated inorganic salts. MAO is a 
solid and is typically kept in solution in toluene. 
Contact of the alumoxane with the support results in a reaction product of 
the alumoxane and the support. When the support is silica, the contact 
product, which can be termed an aluminosilicate, is formed. The reaction 
between the support and the alumoxane occurs via hydroxyl groups of the 
support; thus, if the support is silica, the reaction occurs via silanol 
groups. Confirmation of the formation of this unique product resides in 
two additional independent sources of evidence. First, after contact with 
the support, the alumoxane cannot be extracted off of the support with 
toluene. Second, NMR [nuclear magnetic resonance] spectrum of the product 
shows that a signal unique to alumoxane per se disappears after the 
support is contacted with the alumoxane. 
Contact of the support with alumoxane is undertaken at a -10.degree. C. to 
80.degree. C. temperature range and at ambient pressure. The contact can 
be undertaken in several steps. The amount of alumoxane relative to a 
support is controlled by the available hydroxyl groups on the support or 
by the amount of deposition of alumoxane required. Typically, the amount 
of alumoxane is 2-10 mmol/g support, preferably 4 to 8 mmol/g support. 
This catalyst synthesis step is undertaken under inert conditions, in the 
absence of water and oxygen. 
In one embodiment of the invention, the support is contacted with a 
solution of the alumoxane provided as a volume which is equal to the pore 
volume of the support, so that no slurry of the support is formed during 
the alumoxane/support contact step. Although the presently preferred 
solvent is toluene, it can also be another aromatic hydrocarbon or an 
aliphatic hydrocarbon. 
In a second embodiment of contacting the support with alumoxane, the 
support is used as a slurry in a paraffinic hydrocarbon. In the slurry 
embodiment of making the alumoxane/support contact product, a solvent 
system is used which effects the contact and allows the reaction of the 
support and an alumoxane. In this second embodiment of alumoxane/support 
contact, the total volume of the liquid medium is greater than the pore 
volume of the support. The solvent may be a straight-chain or branched 
alkane containing 5 to 15 carbon atoms selected from the group of 
isohexane, hexane, heptane or isopentane. 
The support is dispersed therein to form a slurry. The total solvent system 
in this case may include one hydrocarbon solvent of 5 to 15 carbon atoms 
or at least two hydrocarbon solvents; in the latter instance, the solvents 
may be miscible and one of them may constitute a solvent for the 
alumoxane, while the second solvent may be a non-solvent for the 
alumoxane. Solvents for the alumoxane include aromatic and aliphatic 
hydrocarbons, preferably toluene. All solvents should be purified, such as 
by percolation through silica gel and/or molecular sieves to remove traces 
of water, oxygen, polar compounds, and other materials capable of 
adversely affecting catalyst activity. 
No isolation of the contact product (A) of a support and an alumoxane is 
required for depositing or impregnating the transition metal derivative 
into the contact product. However, isolation of the support-alumoxane 
contact product (A) is also possible. In the embodiments given below, the 
transition metal complex is added directly to the support-alumoxane 
contact product (A), in situ. 
The transition-metal metallocene complex is deposited or impregnated into 
the contact product (A) as a contact product (B) of an alkylaluminum 
compound and the metallocene complex. Deposition or impregnation of the 
contact product (A) of a support and an alumoxane with the contact product 
(B) comprising a transition metal derivative results in the formation of a 
new contact product; this statement includes a possibility of a chemical 
reaction between the support-alumoxane contact product (A) and the 
transition-metal metallocene complex. 
The transition-metal metallocene compound has the formula Cp.sub.x 
M(R.sup.1).sub.y (R.sup.2).sub.2. This metallocene compound is 
preliminarily contacted with an alkylaluminum compound, preferably a 
trialkylaluminum compound. Metallocene compounds, although not very 
soluble in paraffins, can be readily dissolved in them in the presence of 
a trialkyaluminum compound. The dissolved transition metal compound is 
believed to be a unique chemical entity as metallocene compounds, absent 
the alkyaluminum, are not very soluble in hydrocarbon solvents. The 
alkylaluminum compound: metallocene ratios correspond to molar ratios of 1 
to 100, preferably 5 to 50. Furthermore, the molar ratio of the aluminum, 
provided by the alumoxane, to the transition metal in the metallocene 
complex ranges from 50 to 500, preferably 100 to 300. Contact of these two 
components, a metallocene complex and a trialkylaluminum compound, is 
undertaken in a paraffinic hydrocarbon solvent such as straight-chain or 
branched alkanes containing at least 5 carbon atoms and exemplified by 
pentane, isopentane, hexane, isohexane, n-heptane, and isoheptane. 
The alkylaluminum compound, preferably a trialkylaluminum compound, which 
is contacted with the metallocene compound, is characterized by the 
formula Al(R.sup.3).sub.a (R.sup.4).sub.b (R.sup.5).sub.c, wherein each of 
R.sup.3, R.sup.4, and R.sup.5 is an alkyl group, (straight-chain or 
branched), or a halogen atom, but is preferably an alkyl group containing 
1 to 10 carbon atoms; and each of R.sup.3, R.sup.4, and R.sup.5 is the 
same or different. The alkyl groups can be methyl, ethyl, propyl, 
isopropyl, butyl, isobutyl, pentyl, isopentyl, hexyl, isohexyl, heptyl, 
isoheptyl, octyl, or isooctyl. Most preferably, this component is 
trimethylaluminum (TMA). The alkylaluminum compound, preferably 
trialkylaluminum compound, is contacted with the metallocene compound in 
the absence of alumoxane. This statement means that any product realized 
by the contact of the metallocene compound and a trialkylaluminum compound 
does not involve water and/or an alumoxane. 
The metallocene compound has the formula Cp.sub.x M(R.sup.1).sub.y 
(R.sup.2).sub.Z in which Cp is an unsubstituted or substituted 
cyclopentadienyl group, M is a zirconium, hafnium or titanium atom and 
R.sup.1 and R.sup.2 belong to the group including a halogen atom, a 
hydrogen atom or an alkyl group. In the above formula of the metallocene 
compound, the preferred transition metal atom M is zirconium. In the above 
formula of the metallocene compound, the Cp group is an unsubstituted, a 
mono-, a di-substituted, a tri-substituted or a polysubstituted 
cyclopentadienyl group: and x is at least 1 and preferably is 2. The 
substituents on the cyclopentadienyl group can be preferably 
straight-chain C.sub.1 -C.sub.6 alkyl groups. The cyclopentadienyl group 
can also be a part of a bicyclic or a tricyclic moiety such as indenyl, 
tetrahydroindenyl, fluorenyl or a partially hydrogenated indenyl or 
fluorenyl group, as well as a part of a substituted bicyclic or tricyclic 
moiety. In the case when x in the above formula of the metallocene 
compound is equal to 2, the cyclopentadienyl groups can be also bridged by 
polymethylene or dialkylsilane groups, such as --CH.sub.2 --, --CH.sub.2 
--CH.sub.2, --CR'R"-- and --CR'R"--CR'R"-- where R' and R" are short chain 
alkyl groups or hydrogen atoms, --Si(CH.sub.3).sub.2 --, 
--Si(CH.sub.3).sub.2 --CH.sub.2 --CH.sub.2 --Si(CH.sub.3).sub.2 --, and 
similar bridge groups. If the R.sup.1 and R.sup.2 substituents in the 
above formula of the metallocene compound are halogen atoms, they belong 
to the group of fluorine, chlorine, bromine or iodine; and y+z is 3 or 
less, provided that x+y+z equals the valence of M. If the substituents 
R.sup.1 and R.sup.2 in the above formula of the metallocene compound are 
alkyl groups, they are preferably straight-chain or branched C.sub.1 
-C.sub.8 alkyl groups, such as methyl, ethyl, n-propyl, isopropyl, 
n-butyl, isobutyl, n-pentyl, n-hexyl or n-octyl. 
Suitable metallocene compounds include: 
bis(cyclopentadienyl)metal dihalides, 
bis(cyclopentadienyl)metal hydridohalides, 
bis(cyclopentadienyl)metal monoalkyl monohalides, 
bis(cyclopentadienyl)metal dialkyls and bis(indenyl)metal dihalides wherein 
the metal is a zirconium, hafnium or titanium atom; halide groups are 
preferably chlorine atoms and the alkyl groups are C.sub.1 -C.sub.6 
alkyls. Illustrative but non-limiting examples of metallocenes include 
bis(cyclopentadienyl)zirconium dichloride, 
bis(cyclopentadienyl)hafnium dichloride, 
bis(cyclopentadienyl)titanium dichloride, 
bis(cyclopentadienyl)zirconium dimethyl, 
bis(cyclopentadienyl)hafnium dimethyl, 
bis(cyclopentadienyl)zirconium hydridochloride, 
bis(cyclopentadienyl)hafnium hydridochloride, 
bis(n-butylcyclopentadienyl)zirconium dichloride {(n-BuCp.sub.2 ZrCl.sub.2 
}, 
bis(n-butylcyclopentadienyl)hafnium dichloride, 
bis(n-butylcyclopentadienyl)zirconium dimethyl, 
bis(n-butylcyclopentadienyl)hafnium dimethyl, 
bis(n-butylcyclopentadienyl)zirconium hydridochloride, 
bis(n-butylcyclopentadienyl)hafnium hydridochloride, 
bis(1,3-dimethylcyclopentadienyl)zirconium dichloride, 
ethylenebis(1-indenyl)zirconium dichloride, 
bis(pentamethylcyclopentadienyl)hafnium dichloride, 
cyclopentadienylzirconium trichloride, 
bis(indenyl)zirconium dichloride, 
bis(4,5,6,7-tetrahydro-indenyl)zirconium dichloride, and 
ethylene[bis(4,5,6,7-tetrahydro-1-indenyl )]zirconium dichloride. 
As an example, the contact product (B) of the invention may be prepared 
using (n-BuCp).sub.2 ZrCl.sub.2 and TMA. 
After mixing contact products (A) and (B), to form the final contact 
product, excess solvent is removed by evaporation at an elevated 
temperature. In the process, the soluble metallocene-containing contact 
product (B) becomes affixed to the contact product (A). It is thereafter 
insoluble in same solvent system which was used to prepare the final 
contact product. Preferably the drying temperature is below 90.degree. C. 
and more preferably it is below 60.degree. C. 
The dried catalyst of this invention exists in a particulate form. It can 
be fed to a gas-phase fluidized-bed reactor or to a slurry reactor for 
polymerization and copolymerization of ethylene in the absence of an 
additional alumoxane. 
The temperature of polymerization can range from 25.degree. to 125.degree. 
C., but more generally between 50.degree. and 115.degree. C., at pressures 
of less than 1000 psi. 
The catalyst can be used to produce high density polyethylene but it is 
most commercially valuable for the production of linear low density 
polyethylene (LLDPE) resins in a particulate form. The LLDPE copolymers of 
ethylene and 1-olefins contain at least 80 wt. % ethylene and less than 20 
wt. % of an alpha-olefin of 3 to 10 carbon atoms, preferably of 4 to 10 
carbon atoms, including propylene, 1-butene, 1-pentene, 1-hexene, 
4-methyl-1-pentene, and 1-octene. These LLDPE products exhibit MFR values 
[l.sub.21.6 /l.sub.2.16 ratios, each of which is measured according to 
ASTM D-1238, Conditions F and E] of less than 25.

EXAMPLES 
Example 1 
Into a three-necked flask was added Davison-grade 955 silica (2.50 g) which 
was previously calcined at 600.degree. C. for 4 hours. The dry silica bed 
was stirred and, at ambient temperature, methylalumoxane (MAO) solution in 
toluene (12.50 mmol, about 3 ml) was added to it in a period of 12 
minutes. The liquid was completely absorbed inside the silica pores. After 
stirring the solid bed for about 40 minutes, isohexane (about 100 ml) was 
added to it and the slurry was stirred for about 25 minutes. Separately, a 
heptane solution of a zirconocene complex was prepared by reacting 
trimethylaluminum (TMA) (2.50 mmol) in heptane solution (about 2 ml) with 
(n-BuCp.sub.2)ZrCl.sub.2 (0.0625 mmol, 0.0253 g). This solution was added 
to the above silica-MAO slurry at an ambient temperature. After stirring 
the mixture at ambient temperature for about 45 minutes, the solvents were 
removed by evaporation at about 50.degree. C. under a nitrogen flow to 
yield a pale-yellow, free-flowing powder. 
Example 2 
Into a three-necked flask was added Davison-grade 955 silica (2.50 g) which 
was previously calcined at 600.degree. C. for 4 hours, followed by 
isohexane (100 ml). To this stirred slurry at ambient temperature was 
added MAO solution in toluene (12.50 mmol, about 3 ml). The mixture was 
stirred for 80 minutes at ambient temperature. Separately, a heptane 
solution of a zirconocene complex was prepared by reacting TMA (2.50 mmol) 
in heptane solution (about 2 ml) with (n-BuCp.sub.2)ZrCl.sub.2 (0.0625 
mmol, 0.0253 g). This solution was added to the above asilica-MAO mixture 
at ambient temperature. After stirring the mixture at ambient temperature 
for about 45 minutes, the solvents were removed by evaporation at about 
50.degree. C. under a nitrogen flow to yield a pale-yellow, free-flowing 
powder. 
Example 3 
Into a three-necked flask was added Davison-grade 955 silica (2.50 g) which 
was previously calcined at 600.degree. C. for 4 hours. To this stirred 
silica bed at ambient temperature was added MAO solution in toluene (12.50 
mmol, about 3 ml) in a period of 6 minutes. The liquid was completely 
absorbed inside the silica pores. The solid bed was stirred for about 120 
minutes. Separately, a heptane solution of a zirconocene complex was 
prepared by reacting TMA (2.50 mmol) in heptane solution (about 2 ml) with 
(n-BuCp.sub.2)ZrCl.sub.2 (0.0625 mmol, 0.0253 g). This solution was added 
to the above solid silica-MAO bed at an ambient temperature in a period of 
6 minutes. All the heptane solution was absorbed inside the silica pores. 
After stirring the mixture at ambient temperature for about 30 minutes, it 
was heated at about 50.degree. C. under a nitrogen flow to yield a 
pale-yellow, free-flowing powder. 
Example 4 
Same as Example 2 except 17.50 mmol MAO and 0.0875 mmol (0.0354 g) of 
(n-BuCp.sub.2)ZrCl.sub.2 were used. 
Slurry Polymerization Reactions 
Ethylene/1-hexene copolymers were prepared using catalysts of Examples 1-4 
and an additional amount of a trialkylaluminum compound as an impurity 
scavenger. An example is given below. 
A 1.6-liter stainless-steel autoclave equipped with a magnet-drive impeller 
stirrer was filled with heptane (750 ml) and 1-hexene (165 ml) under a 
slow nitrogen purge at 50.degree. C., and then 2.0 mmol of 
triethylaluminum was added to the reactor. The stirring was increased to 
1000 rpm, and the temperature was increased to 75.degree. C. Then ethylene 
was introduced to maintain the total pressure at about 210 psig. Finally, 
35.8 mg of the catalyst of Example 1 was introduced into the reactor with 
ethylene over-pressure, and the temperature was held at 75.degree. C. The 
polymerization reaction was carried out for one hour and then the ethylene 
supply was stopped. The reactor was cooled to an ambient temperature and 
the polyethylene was collected. 
The slurry polymerization results are given below: 
______________________________________ 
Productivity 
Melt Mole % hexene 
Catalyst g/gh Index MFR in copolymer 
______________________________________ 
Example 1 2410 1.18 18.1 1.90 
Example 2 2710 1.18 17.9 2.15 
Example 3 1630 0.54 16.9 1.90 
Example 4 3330 0.91 17.7 2.25 
______________________________________ 
The data show that the new catalyst systems are highly active. As described 
above, the supported catalysts can be prepared either in the presence or 
in the absence of a saturated hydrocarbon during preparation of contact 
product (A), although higher productivities are obtained when a saturated 
hydrocarbon is employed in the preparative scheme (compare Examples 1 and 
3 with Examples 2 and 4). 
Thus it is apparent that there has been provided, in accordance with the 
invention, a synthesis that fully satisfies the objects, aims, and 
advantages set forth above. While the invention has been described in 
conjunction with specific embodiments thereof, it is evident that many 
alternatives, modifications, and variations will be apparent to those 
skilled in the art in light of the foregoing description. Accordingly, it 
is intended to embrace all such alternatives, modifications, and 
variations as fall within the spirit and broad scope of the appended 
claims.