Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-07-24
2004-09-28
Choi, Ling-Siu (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S348000, C526S113000, C526S124300, C526S158000, C526S169200, C526S908000, C526S904000, C502S103000, C502S104000, C502S117000, C502S115000
Reexamination Certificate
active
06797794
ABSTRACT:
The present invention relates to components of catalysts 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.
Components of high-yield catalysts 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 and low bulk density are experienced when plants operate with catalyst components as such.
In order to solve these problems, the catalyst components are often pre-polymerized under controlled conditions, so as to obtain pre-polymerized catalysts having good morphology. After pre-polymerization, the catalysts also increase their resistance in such a way that the tendency to break under polymerization conditions is decreased. As a consequence, the formation of fines is reduced and the main polymerization process, either in slurry or gas-phase, can be carried out smoothly and with the production of final polymers having high bulk density.
However, one of the possible drawbacks associated with this method is the lowering of the activity expressed as amount of polymer obtained per g of catalyst fed. In other words, even if the activity of the catalyst in itself (expressed in respect of the magnesium chloride contained in the catalyst) could remain at the same level, the activity in respect of the pre-polymer/catalyst system, is lower due to the effect of the dilution of the catalyst within the pre-polymer. Depending on the degree of pre-polymerization, the loss in activity can also be substantial. This means that a large amount of pre-polymer/catalyst system must be fed to the reactor in order to obtain acceptable yields. It would be therefore important to have a pre-polymerized catalyst component in which this drawback is absent or minimized.
In the international patent application WO95/26369 the pre-polymer obtained by pre-polymerization of a catalyst component comprising a Ti compound supported on magnesium dihalide, is contacted with a metallocene compound in particular selected from the class of zirconocenes. The resulting catalyst shows a good activity with respect to magnesium chloride therein contained but the yield is rather low if referred to the pre-polymer/catalyst system. In any case, the catalyst obtained after treatment with the metallocene compound is different in nature from the original conventional Ziegler-Natta catalyst so that also the polymers obtained show the typical features associated with the use of metallocene catalysts such as a very narrow Molecular Weight Distribution. As a consequence, the polymerization results showed in the above-cited patent application do not provide any useful teaching about the possible activity of the original catalyst system contained in the pre-polymer.
The European patent application EP-A-604401 proposes the solution of pre-polymerizing a catalyst component, comprising a titanium compound and an electron donor compound supported on a magnesium dihalide, first with a linear olefin and then with a non linear olefin in order to produce a linear olefin
on linear olefin copolymer as a pre-polymer. The so obtained pre-polymer/catalyst system is further contacted with a Ti compound, in particular TiCl
4
, and optionally also with an electron donor compound in order to obtain a final catalyst component. The pre-polymer/catalyst system obtained however, does not solve the problem because the decrease of the activity observed in the polymerization examples if the activity is calculated as Kg of polymer produced per g of pre-polymer/catalyst fed, is always proportional to the dilution of the catalyst component in the pre-polymer. In other words, when the amount of pre-polymer is about 50% of the total pre-polymer/catalyst system (see Table 2 of EP604401), the activity in the polymerization test is about a half of the activity of the non pre-polymerized catalyst. This means that, according to the disclosure of EP604401, the pre-polymerization step and the further titanation treatment did not improve the activity of the catalyst in itself.
It has now unexpectedly been found a catalyst component having improved activity which is the product obtained by contacting a Ti compound of formula Ti(OR)
n-y
X
y
, where R is an alkyl, isoalkyl, cycloalkyl or aryl radical having from 1 to 18 carbon atoms, preferably an alkyl, isoalkyl or cycloalkyl radical having from 1 to 8 carbon atoms, more preferably n-butyl or isopropyl, X is a halogen atom, preferably a chlorine or bromine atom, n is the valence of titanium and y is a number of from 1 to n, with a pre-polymer having a porosity (measured with Hg method) higher than 0.3 cc/g and containing from 0.5 to 100 g of polymer per g of solid catalyst component, said pre-polymer being obtained by (co)polymerizing an olefin or a diolefin which is (co)polymerizable in the presence of a catalyst comprising a solid component comprising a transition metal compound selected from the group consisting of Ti compounds of the above formula Ti(OR)
n-y
X
y
, vanadium halides, haloalcoholates and vanadyl halides, Ti, Zr and Hf compounds containing at least a &pgr;-metal bond, said transition metal compound being supported on a Mg dihalide having a mean crystallite size lower than 30 nm.
The porosity of the pre-polymer is preferably higher than 0.4 cc/g and still more preferably higher than 0.5 cc/g. In the present application the term (Hg) porosity referred to the pre-polymer means the porosity measured by the mercury porosimetry method described below and due to pores with radius up to 75,000 Å.
The amount of pre-polymer ranges preferably from 1 to 50 and preferably from 2 to 30 g of polymer per g of solid catalyst component used to prepare it.
The term “pre-polymer” used hereabove and hereinafter means a polymer prepared under conditions such as to have a weight ratio polymer/solid catalyst component equal to, or lower than 100; the catalyst used to prepare the pre-polymer being capable to give, under the propylene or ethylene general polymerization conditions given below, a yield higher than 1 Kg/g solid catalyst component.
The magnesium halides, preferably MgCl
2
, in active form used as a support for Ziegler-Natta catalysts, are well known. The active magnesium halides are those having a mean crystallite size, determined by X-ray diffractometry, lower than 30 nm and particularly preferred are those in which the mean crystallite size is lower than 15 nm. Particularly preferred magnesium chlorides are those characterized by X-ray spectra in which the most intense diffraction line that appears in the spectrum of the non-active chloride is diminished in intensity and is replaced by a halo whose maximum intensity is shifted towards lower angles relative to that of the more intense line.
The preparation of the solid catalyst component used to prepar
Sacchetti Mario
Vitale Gianni
Zambon Licio
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