Catalyst

Details Catalyst Catalyst

1999-04-01

2001-06-19

Bell, Mark L. (Department: 1755)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Plural component system comprising a - group i to iv metal...

C502S107000, C502S125000, C502S126000, C502S132000, C502S134000

Reexamination Certificate

active

06248685

ABSTRACT:

THIS INVENTION relates to a catalyst. It relates in particular to a catalyst and catalyst system for use in the polymerization of olefins, to a method of making such a catalyst, and to a method of polymerization.
According to a first aspect of the invention, there is provided a method of making a catalyst suitable for the polymerization of olefins, which method comprises:
mixing an ether having a total number of carbon atoms equal to or greater than 8, with magnesium chloride, to produce partially activated magnesium chloride;
mixing an alkyl aluminium with the partially activated magnesium chloride to form unwashed activated magnesium chloride;
washing the activated magnesium chloride with an inert saturated hydrocarbon liquid, to obtain an activated magnesium chloride-containing slurry;
mixing a plurality of alcohols with the activated magnesium chloride-containing slurry to form an activated magnesium chloride/alcohol complex; and
mixing titanium tetrachloride with the activated magnesium chloride/alcohol complex, to form a magnesium chloride supported titanium catalyst.
Thus, the catalyst obtained by this method is a specific titanium catalyst supported on specifically activated magnesium chloride. The magnesium chloride is hence a catalyst support. The ether and alkyl-aluminium compound mixing steps constitute magnesium chloride support activation steps, while the alcohols and titanium chloride (TiCl
4
) mixing steps constitute catalyst loading steps.
As is known, magnesium chloride forms five hydrates, namely MgCl
2
.12H
2
O, MgCl
2
. 8H
2
O, MgCl
2
.6H
2
O, MgCl
2
.4H
2
O and MgCl
2
.2H
2
O. The most important of these from an application or general use point of view is the hexahydrated form, MgCl
2
.6H
2
O, which is the general raw material used for obtaining, by known methods, MgCl
2
.2H
2
O. It is also known that olefin polymerization processes are influenced detrimentally by even minute amounts of water present in the reaction medium or in a Ziegler-Natta catalyst used in such processes. Attempts to use, in olefin polymerization, known Ziegler-Natta catalysts based on magnesium chloride and containing even a very low proportion of water, have resulted in a decrease in the productivity of olefin polymerization beyond an efficient or practical application. Consequently, substantial effort is normally required to render the hydrated support material completely dry. All these methods are laborious and expensive. In many cases, a drying agent is employed, and some of the drying agent remains as a complex in the resultant catalyst, with undesired consequences on the catalyst performance.
It was surprisingly found that, with catalysts made according to the method of the present invention, limited amounts of water in the magnesium chloride can not only be tolerated, but are in fact desirable for imparting particular properties to the catalyst. The inventors have discovered, surprisingly, that a certain amount of water present in the initial support, if combined using the specific method of catalyst preparation herein described, imparts excellent application properties to the final catalyst. Thus, according to the invention, the magnesium chloride may be partially anhydrized. In other words, the magnesium chloride may have a water content of between 0.02 mole of water/1 mole of MgCl
2
and 2 moles of water/1 mole of MgCl
2
, preferably between 0.08 mole of water/1 mole of MgCl
2
and 0.3 mole of water/1 mole of MgCl
2
. This specified amount of water, by way of its distribution, participates in formation of the specific activated support. For low water content, known magnesium chloride anhydrization methods can be employed, except those where an anhydrization agent remains in the MgCl
2
after washing of the anhydrized magnesium chloride with an inert hydrocarbon liquid. In particular, anhydrization with organic acid esters should be avoided.
The terms “partially anhydrized” and “anhydrous”, as used in respect of magnesium chloride refer to the hydration water limits given above. This precludes side interpretations such as that MgCl
2
.2H
2
O is an “anhydrized” product if compared with MgCl
2
.6H
2
O, or that a 1.5% water containing magnesium chloride is considered “non anhydrous” when compared with a 0.1% water containing magnesium chloride”. Thus, the partially anhydrized magnesium chloride may have a water content of 1.5%, or even 5%, on a mass basis.
The support activation steps are preferably effected under inert conditions, ie in a substantially oxygen and water free reaction environment. The reaction environment should also be substantially free of any reacting products other than the reactants used for each specific step of the catalyst preparation.
In the making or preparation of the catalyst according to the invention, the support activation constitutes a fundamental stage. Attempts to react MgCl
2
directly with TiCl
4
result in hardly any fixation of titanium taking place, probably due to high crystal order, low surface area and low pore volume. Methods to decrease the crystallinity and increase the surface and pore volume of MgCl
2
in general, are known. However, when these methods were employed instead of the catalyst support activation steps used in the present method, a totally different catalyst is obtained, with totally different performances. It was unexpectedly found that only when using the activation procedure as herein described, is a new catalyst, with excellent performance, obtained in the final step.
The activation procedure thus comprises, as hereinbefore stated,
mixing the ether having a total number of carbon atoms equal to or greater than 8, with the magnesium chloride, to produce the partially activated magnesium chloride;
mixing the alkyl aluminium with the partially activated magnesium chloride to form the unwashed activated magnesium chloride; and
washing the activated magnesium chloride with the inert saturated hydrocarbon liquid, to obtain the activated magnesium chloride-containing slurry.
It was also surprisingly found that the desired effect is not achieved with any ether. Thus, the ether is selected from the range of ethers having a total carbon atom number equal to or greater than 8. The ether may be a linear ether with a total number of carbon atoms between 8 and 16, and being of the type R′—O—R″ where R′=R″. Particularly, ethers with a total number of carbon atoms less than 8, are not suitable for the activation procedure hereinbefore described. Moreover, mixtures of ethers each having a total carbon number equal to or greater than 8 can be used. The ether may be dibutyl ether or, preferably, dipentyl ether.
The molar ratio of partially anhydrized magnesium chloride to ether may be between 0.3:1 and 3:1. Preferably, the molar ratio of magnesium chloride to ether is between 1:1 and 2.5:1.
Typical alkyl aluminiums or alkyl-aluminium compounds that can be used are trialkyl-aluminium compounds expressed by the formula AlR
3
wherein R is an alkyl radical or alkyl component having 1 to 10 carbon atoms. Specific examples of suitable trialkyl-aluminium compounds which can be used are tributyl aluminium, tri-isobutyl aluminium, trihexyl aluminium, and trioctyl aluminium. It was surprisingly found that only alkyl-aluminium compounds with no halogen content can be used, to achieve the control of the performances of the newly developed catalyst. The preferred trialkyl-aluminium compound is triethyl-aluminium. The molar ratio of the alkyl-aluminium compound to the anhydrous magnesium chloride may be between 1:1 and 6:1. The preferred molar ratio of the alkyl-aluminium compound to the anhydrous magnesium chloride is 4:1 to 5:1. However, it is an important feature not only of the activation step but also of the specific method of achieving the final complex catalyst that the alkyl aluminium compound be added in a specific amount to suit a specific performance target for the final catalyst.
In one embodiment of this step of the support activation, the molar ratio of the alkyl-aluminium compound to the magnesium ch

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