Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2001-01-02
2003-02-25
Silverman, Stanley S. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S351000, C502S354000
Reexamination Certificate
active
06524995
ABSTRACT:
The present invention relates to novel catalyst systems of the Ziegler-Natta type comprising as active constituents
a) a solid component comprising a compound of titanium or vanadium, a compound of magnesium, a particulate inorganic oxide as support and an internal electron donor compound,
and as cocatalyst
b) an aluminum compound and
c) if desired, a further, external electron donor compound,
wherein the particulate, inorganic oxide used has a specific surface area of from 350 to 1000 m
2
/g and a mean particle diameter {overscore (D)} in the range from 5 to 60 &mgr;m and comprises particles which are composed of primary particles having a mean particle diameter {overscore (d)} in the range from 1 to 10 &mgr;m and contain voids or channels between the primary particles, where the macroscopic proportion of voids or channels having a diameter of greater than 1 &mgr;m in the particles of the inorganic oxides is in the range from 5 to 30% by volume and the molar ratio of the compound of magnesium to the particulate, inorganic oxide is from 0.5:1 to 2.0:1.
The present invention also relates to a process for preparing homopolymers and copolymers of propylene with the aid of such catalyst systems, to the homopolymers and copolymers of propylene obtainable in this way, to their use for producing films, fibers or moldings and to the films, fibers or moldings themselves.
WO 96/05236 describes a supported catalyst component comprising a magnesium halide and, as support, a particulate solid which has a specific surface area of from 10 to 1000 m
2
/g and in which the majority of the support particles are in the form of agglomerates of subparticles. Such catalyst components make it possible to prepare 1-alkene polymers having a good morphology and bulk density at high catalyst efficiency.
EP-A 761 696 relates to catalyst systems of the Ziegler-Natta type comprising, as supports, particulate silica gels which have a mean particle diameter of from 5 to 200 &mgr;m, a mean particle diameter of the primary particles of from 1 to 10 &mgr;m and voids or channels which have a mean diameter of from 1 to 10 &mgr;m and whose macroscopic proportion by volume in the total particle is in the range from 5 to 20%. The catalyst systems have a high productivity and stereospecificity in the polymerization of C
2
-C
10
-alk-1-enes and films produced from such polymers have a reduced tendency to form microspecks, i.e. small irregularities in the surface of the films.
WO 97/48742 discloses loosely aggregated catalyst support compositions which have a particle size of from 2 to 250 &mgr;m and a specific surface area of from 100 to 1000 m
2
/g, where the support particles comprise particles having a mean particle size of less than 30 &mgr;m and a binder which loosely binds these particles to one another. The polymerization catalysts obtainable from such catalyst supports have a high activity and lead to homogeneous polymers from which films having a good appearance can be produced.
WO 97/48743 relates to crumbly, agglomerated catalyst support particles which have a mean particle size of from 2 to 250 &mgr;m and a specific surface area of from 1 to 1000 m
2
/g and which are produced by spray drying primary particles having a mean particle size of from 3 to 10 &mgr;m. The characteristic feature of these agglomerated catalyst support particles is that at least 80% by volume of the agglomerated particles which are smaller than the D
90
of the original particle size distribution have a microspherical morphology. (The D
90
indicates that 90% by volume of the particles have a smaller diameter.) The microspherical agglomerated catalyst support particles have interstitial voids of uniform size and distribution within the particle; at least some of the voids penetrate the particle surface and thus form at least 10 channels from the surface to the interior of the agglomerated particles. The polymerization catalysts obtainable from these catalyst supports also have a high activity and allow the production of films having a good appearance.
Although the polymers prepared using polymerization catalysts corresponding to the prior art described by and large meet the requirements in respect of film quality, the proportion of microspecks or troublesome impurities is still capable of significant improvement, especially compared to polymers which have been produced using catalyst systems containing no inorganic oxides as support.
Furthermore, in the production of fibers from polymers of propylene, it is necessary for economic reasons to achieve a significant increase in the operating lives of the filters for liquid polypropylene upstream of the spinnerets. These operating lives are significantly lower in the case of polypropylene which has been prepared using supported catalysts than in the case of polypropylene which has been obtained using an unsupported catalyst.
However, the advantages in respect of polymer morphology which result from the use of the inorganic oxides should be retained. In addition, there is always a need to achieve higher catalyst productivities.
It is an object of the present invention to remedy the abovementioned disadvantages and to develop improved catalyst systems of the Ziegler-Natta type which have significantly improved productivity and which make it possible to obtain polymers of 1-alkenes having a good morphology and a high bulk density from which it is possible to produce, inter alia, films having a reduced tendency to form microspecks and fibers having less troublesome contamination, which leads to an increase in the operating lives of the polymer melt filtration screens.
We have found that this object is achieved by the catalyst systems defined at the outset, and also by the process for preparing polymers of propylene, their use for producing films, fibers or moldings and also the films and fibers or moldings made of these polymers.
The catalyst systems of the present invention comprise a solid component a) and also a cocatalyst. A suitable cocatalyst is the aluminum compound b). Preferably, in addition to this aluminum compound b), an electron donor compound c) is additionally used as a further constituent of the cocatalyst.
According to the present invention, the catalyst system is prepared using at least one particulate inorganic oxide which has a specific surface area of from 350 to 1000 m
2
/g, preferably from 400 to 700 m
2
/g and in particular from 450 to 600 m
2
/g, determined by nitrogen adsorption in accordance with DIN 66131.
The inorganic oxides to be used according to the present invention have a mean particle diameter {overscore (D)} of from 5 to 60 &mgr;m, preferably from 15 to 60 &mgr;m and in particular from 20 to 60 &mgr;m. Here, the mean particle diameter {overscore (D)} is the volume-based mean (median) of the particle size distribution determined by Coulter Counter analysis in accordance with ASTM Standard D 4438.
The particles of the inorganic oxides are composed of primary particles which have a mean particle diameter {overscore (d)} of from 1 to 10 &mgr;m, preferably from 3 to 10 &mgr;m and in particular from 4 to 8 &mgr;m. These primary particles are porous, granular oxide particles which are generally obtained by dry and/or wet milling from a hydrogel of the inorganic oxide. It is also possible to sieve the primary particles before they are processed further.
In addition, the inorganic oxides have voids or channels which have a diameter of greater than 1 &mgr;m and whose macroscopic proportion in the particles of the inorganic oxides is in the range from 5 to 30% by volume, in particular from 10 to 25% by volume. It is also advantageous for them to meet at least one of the following conditions:
i) less than 10% by volume and preferably less than 8% by volume of the primary particles have a particle diameter d of greater than 15 &mgr;m or
ii) less than 5% by volume and preferably less than 3% by volume of the primary particles have a particle diameter d of greater than 20 &mgr;m.
The mean particle diameter {overscore (d)} of the primary particles, the distribution of the
Bidell Wolfgang
Hemmerich Rainer
Hingmann Roland
Hüffer Stephan
Lynch John
Basell Polypropylene GmbH
Johnson Edward M.
Keil & Weinkauf
Silverman Stanley S.
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