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
2002-07-29
2004-11-16
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...
C502S110000, C502S115000, C502S128000, C502S132000, C526S124300
Reexamination Certificate
active
06818584
ABSTRACT:
This invention relates to a new process for preparing a Ziegler-Natta catalyst and in particular to a simple solution phase process which can be carried out in one reaction vessel.
Ziegler-Natta type polyolefin catalysts have been known since the early 1950's and general methods of their making and subsequent use are well known in the field of polymers.
The use of Ziegler-Natta catalysts in multiple step polymerisation of olefins however often results in the production of a polymer containing undesirable inhomogeneities, e.g. gels and white dots.
Ziegler-Natta catalysts are generally formed from two components: a compound of a transition metal belonging to groups 4 to 6 of the Periodic Table, often called the procatalyst; and a compound of a metal belonging to groups 1 to 3 of the Periodic Table. Such catalyst compositions have been further developed by depositing the procatalyst on a particulate support and by adding various additives such as electron donating groups.
There has been much research into different methods of preparing Ziegler-Natta catalysts and how differing reaction conditions may result in polymer products with differing properties. There remains however, a continuing search for new methods of preparing Ziegler-Natta catalysts with improved properties.
One conventional route of preparing Ziegler-Natta catalysts is to use a particulate support throughout the synthesis. For example, in EP-A-688794 a process is disclosed in which a support is contacted with an alkyl metal chloride, the resulting product is contacted with a magnesium compound and the product of this second stage is contacted with a titanium chloride. The reactions in this synthesis obviously take place on the surface of or in the neighbourhood of the support. In such a synthesis, the individual reaction steps may proceed differently depending on the nature of the interaction with the support. This may lead to non-uniform active sites and in turn to inhomogeneous polymer material. Recently however, a number of solution phase syntheses of Ziegler-Natta catalysts have been proposed.
In U.S. Pat. No. 5,817,591, a process for producing Ziegler-Natta polymerisation catalysts from magnesium alkoxy chloride is described. The magnesium alkoxy chloride is dissolved in a hydrocarbon solvent with the addition of an alcohol before the solution is contacted with titanium tetrachloride to give a precipitate. This precipitate is converted into the catalyst upon the addition of further titanium tetrachloride and of butyl phthalate.
In EP-A-22376 a catalyst is prepared by suspending magnesium dichloride in hexane and adding ethanol, followed by diethyl aluminium chloride followed by titanium tetrachloride.
Both these methods involve a magnesium compound which is insoluble in hydrocarbon solvents, a further reagent being required to ensure the magnesium compound is solubilised. The inventors of the present invention have surprisingly found that preparing Ziegler-Natta catalysts from a magnesium compound which is essentially soluble in an inert hydrocarbon solvent results in high catalyst activity, the production of homogeneous olefin polymers with low levels of gels and other impurities such as white dots, and the reduction of residual levels of reagents from catalyst production.
In U.S. Pat. No. 5,589,555 a Ziegler-Natta catalyst in solution is prepared by mixing dibutylmagnesium, triethylaluminium, tertiarybutylchloride and titanium tetrachloride in, for example, cyclohexane in one reaction vessel. The resulting catalyst composition is then used directly as a Ziegler-Natta catalyst. While this kind of strongly reduced catalyst is suitable for a solution polymerization process operating at a high temperature and a short residence time, it is less suitable for a suspension polymerization process operating at a relatively low temperature and having a longer residence time. For example the polymerization activity of this type of catalyst tends to decay rapidly with time and the activity at lower polymerization temperatures is usually low.
It has now been surprisingly found that especially homogeneous supported Ziegler-Natta catalysts may be prepared in a simple one reaction vessel process from a magnesium hydrocarbyloxy starting material which is soluble in a hydrocarbon solvent. By preparing the Ziegler-Natta catalyst in the solution phase before impregnating the final solution into a support, a much more homogeneous catalyst product is obtained. Clearly, the impregnating solution allows even and homogeneous impregnation into the support thus enabling production of a catalyst giving a more homogeneous polymer. Moreover, the entire process may take place in a single reaction vessel giving both process and economic advantages over prior art catalysts.
Thus, viewed from one aspect the invention provides a process for the preparation of a Ziegler-Natta catalyst comprising the steps of:
(I) reacting a magnesium hydrocarbyloxy compound, with a chlorine-containing compound (e.g. HCl, or more preferably a chlorine-containing metal alkyl compound, most preferably a chlorine-containing aluminium alkyl compound) in a non-polar hydrocarbon solvent in which said magnesium hydrocarbyloxy compound is soluble whereby to produce a solution (A);
(II) contacting the solution (A) with a chlorine containing tetravalent titanium compound to produce a solution (B); and optionally
(III) impregnating solution (B) into a porous particulate support.
Viewed from another aspect the invention provides a Ziegler-Natta catalyst obtained by the process as hereinbefore described.
The magnesium hydrocarbyloxy compound used in the preparation of solution (A) is conveniently a magnesium hydrocarbyl hydrocarbyloxy compound, a magnesium dihydrocarbyloxy compound, a magnesium hydrocarbyloxy chloride compound or a magnesium hydrocarbyl hydrocarbyloxy chloride compound, i.e. a compound of formula 1
MgR
x
(OR)
y
Cl
z
(1)
where x and z are zero or positive numbers which may or may not be integers, each independently having values of less than 2, y is a positive number having a value of up to 2 and the sum of x, y and z is 2; and each R independently represents a C
1-20
hydrocarbyl group preferably a C
2-15
group, especially a C
3-10
group and more preferably a C
4-8
group, e.g. an alkyl, aryl, aralkyl or alkaryl group, for example an ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 2-methyl-hexyl or 2-ethyl-hexyl group, especially a linear alkyl group. The magnesium hydrocarbyloxy compound may moreover be a magnesium hydrocarbyl alcohol adduct.
The magnesium hydrocarbyloxy compound is used in solution and hence, as will be understood from the above, may be a mixed compound in which the ratio of Mg to R, to OR or to Cl is a non-integer. In general, for the magnesium hydrocarbyloxy compound to be soluble in the hydrocarbon solvent, where y is large then z or/and x will correspondingly be small. In other words the OR groups essentially serve to solubilize the compounds. Solubilisation may likewise be enhanced by increased disorder, i.e. by the use of non-identical R groups or by the use of R groups of similar structure to the hydrocarbon solvent, for example by the use of aromatic R groups if the solvent is aromatic.
Magnesium hydrocarbyloxy compounds usable in the process of the invention may be produced for example by reaction of magnesium dihydrocarbyl (e.g. dialkyl) compounds with alcohols (i.e. hydrocarbyl alcohols), optionally followed by reaction with a chlorinating agent, for example a hydrocarbyl aluminium chloride (such as for example ethyl aluminium dichloride). The desired values of x, y and z may be achieved by selecting the molar ratios of magnesium dihydrocarbyl compound to alcohol and to chlorinating agent. Likewise magnesium hydrocarbyloxy chlorides in which x is zero and z is non-zero may be produced by reacting a magnesium dihydrocarbyloxy compound with a chlorinating agent.
Suitable magnesium dialkyl starting compounds include dibutyl magnesium, butyl-octyl magnesium, and butyl-ethyl magnesium.
Suitable magnesium dial
Garoff Thomas
Johansson Solveig
Waldvogel Paivi
Bell Mark L.
Borealis Technology OY
Brown Jennine M
Nixon & Vanderhye P.C.
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