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
1999-03-23
2002-10-22
Wood, Elizabeth D. (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...
C502S103000, C502S104000, C502S112000, C502S113000, C502S115000, C502S116000, C502S118000, C502S128000
Reexamination Certificate
active
06468938
ABSTRACT:
The present invention relates to catalyst components for the polymerization of olefins CH
2
═CHR, wherein R is hydrogen or a hydrocarbon radical having 1-12 carbon atoms, the catalysts obtained therefrom and their use in the polymerization of said olefins. In particular the catalyst components of the present invention are very suitable for the preparation of crystalline propylene (co)polymers by using gas-phase, slurry or bulk (co)polymerization processes.
High-yield catalyst components for the polymerization of olefins and in particular for propylene are known in the art. They are generally obtained by supporting, on a magnesium dihalide, a titanium compound and an electron donor compound as a selectivity control agent. Said catalyst components are then used together with an aluminum alkyl and, optionally, another electron donor (external) compound in the stereospecific polymerization of propylene. Depending on the type of electron donor used the stereoregularity of the polymer can vary. However, the stereospecific catalysts of interest should be able to give polypropylene (co)polymers having isotactic index, expressed in terms of xylene insolubility, of higher than 90%.
Said catalyst components, and the catalysts obtained therefrom, are largely used in the plants for the (co)polymerization of propylene both operating in liquid phase (slurry or bulk) and in gas-phase. However, the use of the catalyst components as such is not completely satisfactory. Indeed, problems such as formation of polymers with irregular morphology and in particular of fines, low bulk density and low catalyst activity are experienced when plants operate with catalyst components as such.
In order to solve these problems, an additional prepolymerization line may be included, in which the catalyst is prepolymerized under controlled conditions, so as to obtain prepolymerized catalysts having good morphology. After prepolymerization, the catalysts also increase their resistance in such a way that the tendency to break under polymerization conditions is decreased. As a consequence, also the formation of fines is reduced. Moreover also the activity of the catalyst and the bulk density of the final polymers results to be improved. The use of this additional line, however, makes the plant operations and design more complex and costly; in certain cases it is therefore desirable to avoid it.
One of the alternative solutions is that of supplying the plants directly with a prepolymerized catalyst which can be prepared in another facility. This solution requires the preparation of a prepolymerized catalyst meeting certain requirements such as easy preparation and handling, easy stocking operability, absence or minimal reduction of activity with time (aging) preferably coupled with a basic high activity. U.S. Pat. No. 5,641,721 discloses a method for preparing a prepolymerized catalyst comprising (i) the preparation of a procatalyst composition by depositing a transition metal compound on a suitable support, (ii) mixing said procatalyst composition with a viscous substance and then prepolymerizing said procatalyst composition with a monomer in the presence of said viscous substance. The viscous substance has a viscosity of from 1000 to 15000 cP while the monomer used is propylene. Albeit it is alleged that the catalyst activity is unchanged after 5 months, it appears that the selectivity is decreased. Moreover, the prepolymerization in such a viscous substance makes the preparation of the prepolymerized catalyst complex and, in addition, leads to a low catalyst activity.
It has now surprisingly been found that by carrying out the prepolymerization with a specific monomer it is possible to obtain a catalyst for the polymerization of olefins which has a high catalyst activity, a high isotactic index and which is not affected by aging.
It is therefore an object of the present invention a prepolymerized catalyst component for the (co)polymerization of olefins CH
2
═CHR, wherein R is hydrogen or a C1-C12 alkyl group, characterized by comprising a solid catalyst component, comprising Ti, Mg, halogen and an electron donor compound, being capable of yielding, under standard polymerization conditions, a propylene homopolymer having an insolubility in xylene at 25° C. higher than 90%, which is prepolymerized with ethylene to such an extent that the amount of the ethylene prepolymer is up to 100 g per g of said solid catalyst component. Preferably the amount of ethylene polymer is less than 15 g and more preferably said amount is less than 5 g per g of solid catalyst component.
In particular, the catalyst components comprise a titanium compound, having at least a Ti-halogen bond and the above mentioned electron donor compound supported on a Mg halide. The magnesium halides, preferably MgCl
2
, in active form used as a support for Ziegler-Natta catalysts, are widely known from the patent literature. Patents U.S. Pat. No. 4,298,718 and U.S. Pat. No. 4,495,338 were the first to describe the use of these compounds in Ziegler-Natta catalysis. It is known from these patents that the magnesium dihalides in active form used as support or co-support in components of catalysts for the polymerization of olefins are characterized by X-ray spectra in which the most intense diffraction line that appears in the spectrum of the non-active halide is diminished in intensity and is replaced by a halo whose maximum intensity is displaced towards lower angles relative to that of the more intense line.
The preferred titanium compounds used in the catalyst component of the present invention are TiCl
4
and TiCl
3
; furthermore, also Ti-haloalcoholates of formula Ti(OR)
n−y
X
y
, where n is the valence of titanium and y is a number between 1 and n, can be used.
The internal electron-donor compound may be selected from esters, ethers, amines and ketones. It is preferably selected from alkyl, cycloalkyl or aryl esters of monocarboxylic acids, for example benzoic acid, or polycarboxylic acids, for example phthalic or malonic acid, the said alkyl, cycloalkyl or aryl groups having from 1 to 18 carbon atoms. Moreover, it can be also selected from 1,3-diethers of formula (I):
wherein R
I
, R
II
, R
III
, R
IV
, R
V
and R
VI
equal or different to each other, are hydrogen or hydrocarbon radicals having from 1 to 18 carbon atoms, and R
VII
and R
VIII
, equal or different from each other, have the same meaning of R
I
-R
VI
except that they cannot be hydrogen; one or more of the R
I
-R
VIII
groups can be linked to form a cycle. Particularly preferred are the 1,3-diethers in which R
VII
and R
VIII
are selected from C
1
-C
4
alkyl radicals.
Examples of preferred electron-donor compounds are methyl benzoate, ethyl benzoate, diisobutyl phthalate and 9,9-bis(methoxymethyl)fluorene. As explained above, however, the internal electron donor compound must be selected in such a way to have a final solid catalyst component capable of producing, under the standard polymerization test disclosed below, a propylene homopolymer having an insolubility in xylene at 25° C. higher than 90%.
The preparation of the solid catalyst component can be carried out according to several methods. According to one of these methods, the magnesium dichloride in an anhydrous state, the titanium compound and the electron donor compound of formula (I) are milled together under conditions in which activation of the magnesium dichloride occurs. The so obtained product can be treated one or more times with an excess of TiCl
4
at a temperature between 80 and 135° C. This treatment is followed by washings with hydrocarbon solvents until chloride ions disappeared. According to a further method, the product obtained by co-milling the magnesium chloride in an anhydrous state, the titanium compound and the electron donor compound is treated with halogenated hydrocarbons such as 1,2-dichloroethane, chlorobenzene, dichloromethane etc. The treatment is carried out for a time between 1 and 4 hours and at temperature of from 40° C. to the boiling point of the halogenated hydrocarbon. Th
Govoni Gabriele
Sacchetti Mario
Vitale Gianni
Basell Technology Company BV
Bryan Cave LLP
Wood Elizabeth D.
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