Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Plural component system comprising a - group i to iv metal...
Reexamination Certificate
1998-10-02
2001-05-29
Wu, David W. (Department: 1713)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Plural component system comprising a - group i to iv metal...
C502S152000, C526S160000, C526S943000
Reexamination Certificate
active
06239059
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an activator solid support for metallocene catalysts used for the polymerization of olefins, to a process for preparing such a support, to the corresponding catalytic system and to the suspension or gas-phase polymerization of olefins using such a catalytic system.
BACKGROUND OF THE INVENTION
It is well known to (co)polymerize ethylene and &agr;-olefin in the presence of a metallocene/aluminoxane catalyst system. The first very active catalytic system of this type that was discovered is that based on zirconocene: Cp
2
ZrCl
2
/aluminoxane. Metallocene/aluminoxane catalyst systems are soluble in the polymerization medium. The extension of research in this field has led to the discovery of other metallocene catalysts, such as bridged metallocenes which are capable, in the case of the copolymerization of ethylene with &agr;-olefins, of leading to better uniformity in the distribution of the comonomers in the molecular chains.
However, aluminoxanes, in particular methylaluminoxane which is the most commonly used, have the drawbacks of being expensive and unstable substances which are partly responsible for the poor morphology of the polymers, a situation which causes fouling of the reactors and which makes the conveying process very complicated.
DESCRIPTION OF THE INVENTION
Applicant has sought to solve this problem for the purpose of providing a metallocene-based catalytic system, which is active for the polymerization of olefins and does not use aluminoxane, or uses less aluminoxane than in the past.
It is now accepted that a metallocene complex has a cationic nature in its active form. This has been confirmed by several spectroscopic methods and by the equivalence of the properties of two polymers, one produced by the metallocene/aluminoxane system and the other produced by metallocene/stable cationic salt systems. The role of the aluminoxane is assumed to be the alkylation of the metallocene, the activation of the methylated species by the formation of a cationic complex and the stabilization of this active species. Many non-coordinating counteranions have been proposed for replacing the aluminoxane in its activator role [J. Ewen, M. Elder, R. Jones, L. Haspeslagh, J. Atwood, S. Bott and K. Robinson, Makromol. Chem. Macromol. Symp. 48/49, 253 (1991) and M. Bochmann and S. Lancaster: Organometallics, 12, 633 (1993)].
Applicant has discovered that the counteranion of the active cationic complex could consist of a solid support, advantageously having a defined and controlled structure comparable to that of the supports employed in conventional Ziegler-Natta catalysis in order to allow physical development of the polymerization, the said support being functionalized in order to create acid sites which activate the metallocene without complexing it.
The solid support according to the invention, as defined below, constitutes an activator support which has made it possible to reach levels of activity, in the polymerization of olefins, at least equal to, but often greater than, the activity displayed by a purely homogeneous system.
The subject of the present invention is therefore firstly an activator solid support for metallocenes as catalysts in the polymerization of olefins, characterized in that it consists of a group of support particles for a solid catalytic component, which are formed from at least one porous mineral oxide, the said particles having been modified in order to carry, on the surface, aluminium and/or magnesium Lewis-acid sites of formula:
functionalization agent having reacted with —OH radicals carried by the base particles of the support, the functionalization reaction having been followed by a fluorination reaction.
The direct use of aluminium and/or magnesium fluorides presents difficulties which are barely surmountable in terms of forming a support having suitable particle-size and porosity properties.
The porous mineral oxides are advantageously chosen from silica, alumina and mixtures thereof.
The porous mineral oxide particles preferably have at least one of the following characteristics:
they include pores having a diameter ranging from 7.5 to 30 nm (75 to 300 Å);
they have a porosity ranging from 1 to 4 cm
3
/g;
they have a specific surface area ranging from 100 to 600 m
2
/g; and
they have an average diameter ranging from 1 to 10 &mgr;m.
Before it is modified, the support has —OH radicals on its surface, in particular from 0.25 to 10, and even more preferably from 0.5 to 4 —OH radicals, per nm
2
. After it has been modified, the said support has as many at least partially fluorinated aluminium and/or magnesium Lewis-acid sites per nm
2
.
The support may be of various kinds. Depending on its nature, its state of hydration and its ability to retain water, it is possible to make it undergo dehydration treatments of greater or lesser intensity depending on the desired surface content of —OH radicals.
Those skilled in the art may determine, by routine tests, the dehydration treatment that should be applied to the support that they have chosen, depending on the desired surface content of —OH radicals.
For example, if the support is made of silica, which is in accordance with a preferred embodiment of the invention, the silica may be heated between 100 and 1000° C. and preferably between 140 and 800° C., with purging by an inert gas such an nitrogen or argon, at atmospheric pressure or under a vacuum, for example of an absolute pressure of 1×10
−2
millibars, for at least 60 minutes, for example. For this heat treatment, the silica may be mixed, for example, with NH
4
Cl so as to accelerate the dehydration.
If this heat treatment is between 100 and 450° C., it is conceivable to follow it with a silanization treatment. This kind of treatment results in a species derived from silicon being grafted on the surface of the support in order to make this surface more hydrophobic. This silane may, for example, be an alkoxytrialkylsilane, such as methoxytrimethylsilane, or a trialkylchlorosilane, such as trimethylchlorosilalne or triethylchlorosilane.
This silane is generally applied to the support by forming a suspension of this support in an organic silane solution. This silane may, for example, have a concentration of between 0.1 and 10 mol per mole of OH radicals on the support. The solvent for this solution may be chosen from linear or branched aliphatic hydrocarbons, such as hexane or heptane, alicyclic hydrocarbons, optionally substituted, such as cyclohexane, and aromatic hydrocarbons, such as toluene, benzene or xylene. The treatment of the support by the silane solution is generally carried out between 50° C. and 150° C., for 1 to 48 hours, and with stirring.
After silanization, the solvent is removed, for example, by siphoning or filtration, the support then being washed, preferably thoroughly, for example using 0.3 l of solvent per gram of support.
The surface —OH radical content of the support may be assayed using known techniques such as, for example, by reacting an organomagnesium compound such as CH
3
MgI with the support and by measuring the amount of methane given off [McDaniel, J. Catal., 67, 71 (1981)]; by reacting triethylaluminium with the support and by measuring the amount of ethane given off [Thesis of Véronique Gachard-Pasquet, Université Claude Bernard, Lyon 1, France, 1985, pages 221-224].
According to the present invention, the said at least partially fluorinated aluminium and/or magnesium Lewis-acid sites are formed by the reaction of —OH radicals carried by the support base particles with at least one functionalization agent chosen from:
compounds of formula (I):
Al(R
1
)
3
(I)
in which the R
1
groups, which are identical or different, each represent a C
1
-C
20
alkyl group;
compounds of formula (II):
Mg(R
2
)
2
(II)
in which the R
2
groups, which are identical or different, each represent a C
1
-C
12
, alkyl group; and
compounds of formula (III):
in which
the R
3
groups, which are identical or different, eac
Broyer Jean-Pierre
Malinge Jean
Saudemont Thierry
Spitz Roger
Verdel Nathalie
Elf Atochem S.A.
Lu Caixia
Smith , Gambrell & Russell, LLP
Wu David W.
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