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
1999-04-22
2001-04-24
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...
C502S132000, C502S133000, C502S134000, C502S103000
Reexamination Certificate
active
06221803
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a Ziegler-Natta type catalyst, a process for preparing such a catalyst and its use in polyolefin production.
BACKGROUND TO THE INVENTION
It is known that anhydrous magnesium dichloride derivatives which are suitable for the preparation of Ziegler-Natta catalysts can be obtained by reacting an organo magnesium or a Grignard reagent with a halogenated compound. For example, U.S. Pat. No. 4,186,107, and its equivalent FR-A-2464965, each describe the synthesis of a catalyst composed of a titanium halide deposited on a magnesium halide support. The support may be prepared by reacting a dialkyl magnesium with an alkyl aluminium halide in a hydrocarbon solvent. The support may be treated with an electron donor such as a dialkyl ether in order to provide a means for controlling its morphology. Very low temperatures are preferred in the synthesis of the catalyst and all the examples were conducted at around −65° C. This presents a serious disadvantage in the industrial applicability of this method.
EP-A-98196 reports the synthesis of magnesium dichloride catalyst supports having spherical particles of controllable size distribution by reacting a dialkyl magnesium with an alkyl chloride in the presence of an electron donor, preferably an ether.
EP-A-68200 describes a process for the production of granular ethylene polymers having a large, uniform particle size and a high bulk density. An organic magnesium compound is reacted with a hydropolysiloxane or a silicon compound to give a silicon-containing reaction product which is then reacted with the reaction product of an organic aluminium chloride compound with a mixture of alcohols. The product of this reaction is further reacted with a halogen-containing titanium or vanadium compound. This approach is further developed in U.S. Pat. No. 4,223,118 which also requires the use of the reaction product of an organic magnesium compound with a hydropolysiloxane or silicon compound. This silicon-containing reaction product is further reacted with an aluminium alkoxide which optionally contains a halogen atom. These processes suffer from a disadvantage that complex synthetic procedures are required to achieve the desired catalyst.
EP-A-093454 reports a solid catalyst component for alpha-olefin polymerisation made by reacting a magnesium compound such as n-butyl, sec-butyl-magnesium with a catalyst such as obtained by reacting aluminium chloride with ethyl benzoate. No steps are taken to control the morphology or particle size distribution of the solid catalyst component.
U.S. Pat. No. 4,873,300 reports a catalyst preparation by reacting with a reducing halide source a mixture of a hydrocarbon soluble magnesium alkyl compound, an aliphatic alcohol and a titanium compound.
SUMMARY OF THE INVENTION
The present invention provides a process for preparing a Ziegler-Natta catalyst, which process comprises:
(i) mixing in a hydrocarbon solvent a dialkyl magnesium compound of general formula MgR
1
R
2
with a chlorinating agent soluble in the hydrocarbon solvent under conditions to precipitate controlledly a magnesium dichloride derivative, wherein R
1
and R
2
are each independently a C
1
to C
10
alkyl group preferably a C
2
to C
8
alkyl group, and the chlorinating agent is obtainable from the reaction between an alcohol of general formula R
3
OH and an alkyl aluminium chloride of general formula R
4
n
AlCl
3−n
, in which R
3
OH is a cyclic or branched C
3
to C
20
alcohol, each R
4
is independently a C
2
to C
8
alkyl and n is 1 or 2; and
(ii) titanating the magnesium dichloride derivative with a chlorinated titanium compound to produce the Ziegler-Natta catalyst.
The catalyst obtainable by this process produces polyolefins, especially polyethylene homopolymers or copolymers, with a low amount of fines of less than 125 &mgr;m, no agglomerates of greater than 1600 &mgr;m, a narrow particle size distribution, a high bulk density and a regular shape. Moreover, the catalyst has high activity and high sensitivity versus hydrogen.
The dialkyl magnesium compound is preferably n-butyl sec-butyl magnesium or butyl ethyl magnesium although other dialkyl magnesium compounds such as butyl octyl magnesium, dibutyl magnesium and dihexyl magnesium can be used. The dialkyl magnesium derivative should be soluble in the hydrocarbon solvent used in the process.
The chlorinating agent obtainable from the reaction between the alcohol and the alkyl aluminium chloride may have the general structure (R
3
O)
n
AlCl
3−n
, preferably (R
3
O)
2
AlCl. The alcohol is selected such that, after reaction with the alkyl aluminium chloride, the chlorinating agent product is a compound soluble in the hydrocarbon solvent used in the process. This is important for particle size and particle size distribution control. The alcohol may be 2-ethyl-1-hexanol, 2-methyl-1-pentanol, 2-ethyl-1-butanol, 2-methyl-2-propanol, 2-methyl-1-propanol, cyclopentanol or cyclohexanol, preferably 2-ethyl-1-hexanol. The preferred alkyl aluminium chloride is diethyl aluminium chloride.
The molar ratio of the alcohol to the alkyl aluminium chloride is usually from 0.5 to 2.5, preferably about 2. The molar ratio of the alkyl aluminium chloride to the dialkyl magnesium compound is usually in the range of from 0.8 to 2.2.
Other methods of making compounds of the formula (R
3
O)
n
AlCl
3−n
include reacting together an alkoxy aluminium derivative Al(OR
3
)
3
, such as aluminium ethoxide or isopropoxide, with a chlorinating agent, typically an acyl halide such as acetyl chloride.
Any non-aromatic hydrocarbon solvent may be used in the process although, from a practical viewpoint, it is usual for the solvent to be removed subsequently. Hydrocarbon solvents of less than 6 carbon atoms tend to boil too easily whereas hydrocarbon solvents having more than 7 carbon atoms are often difficult to remove. Accordingly, preferred hydrocarbon solvents are hexane or heptane.
In step (ii) any chlorinated titanium compound suitable for titanating the magnesium dichloride derivative may be used. Such chlorinated titanium compounds include TiCl
4
, TiCl
3
OR
5
, TiCl
2
OR
5
2
, TiClOR
5
3
, or mixtures thereof, in which each R
5
is independently a C
2
to C
8
alkyl, preferably TiCl
4
.
A dialkyl ether may be added into the process to improve the fluff bulk density achieved during polyolefin synthesis. Preferably, the dialkyl magnesium compound is premixed in the hydrocarbon solvent with an acyclic dialkyl ether of general formula R
5
—O—R
6
, in which R
5
and R
6
are each independently C
2
to C
10
alkyl groups. Preferably, the dialkyl ether is diisoamyl ether. The molar ratio of the dialkyl magnesium compound to the dialkyl ether is preferably 1.93. The ether is used to increase the polyolefin fluff bulk density but has little or no influence on the catalyst granulometry or particle size distribution.
Turning to the general procedure for preparing the Ziegler-Natta catalyst, the dialkyl magnesium compound may be dissolved in the hydrocarbon solvent and mixed with the dialkyl ether at room temperature to form a solution. The alcohol may be added to the alkyl aluminium chloride which is dissolved in the hydrocarbon solvent to form a solution. This solution may be left at room temperature for a period of at least 0.5 hours so as to ensure that a reaction takes place between the alcohol and the alkyl aluminium chloride to form the chlorinating agent. Alternatively, the dialkyl magnesium compound and the chlorinating agent may be added to the solvent at the same time. However normal, the reaction mixture can be stored under an inert atmosphere for of the order of 4 to 6 days without degradation.
The solution of the chlorinating agent, usually in the hydrocarbon solvent, is mixed rapidly with a solution of the dialkyl magnesium compound in the hydrocarbon solvent, for example by dropwise addition, so as to achieve mixing with controlled precipitation. Under these conditions, the “MgCl
2
” precipitation proceeds very slowly and a good control of the
Bell Mark L.
Fina Research S.A.
Pasterczyk J.
Wheelington Jim D.
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