Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-02-16
2003-09-30
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, C526S119000, C526S123100, C526S124200, C526S124300, C526S142000, C502S103000, C502S119000, C502S125000, C502S134000
Reexamination Certificate
active
06627710
ABSTRACT:
The present invention relates to catalyst components for the polymerization of olefins CH
2
═CHR, wherein R is hydrogen or hydrocarbon radical having 1-12 carbon atoms. In particular, the invention relates to catalyst components suitable for the preparation of homopolymers and copolymers of ethylene having a broad molecular weight distribution (MWD), and to the catalysts obtained therefrom.
In particular the present invention relates to a solid catalyst component, comprising titanium magnesium and halogen, having spherical morphology and particular surface characteristics. Furthermore, the present invention relates to a process for preparing ethylene homopolymers and copolymers characterized by a high melt flow ratio (F/E) value, which is the ratio between the melt index measured with a 21.6 Kg load (melt index F) and the melt index measured with a 2.16 Kg load (melt index E), determined at 190° C. according to ASTM D-1238. Said ratio F/E is generally considered as an indication of the width of molecular weight distribution. The MWD is a particularly important characteristic for ethylene (co) polymers, in that it affects both the rheological behavior and therefore the processability of the melt, and the final mechanical properties. Polyolefins having a broad MWD, particularly coupled with relatively high average molecular weights, are preferred in high speed extrusion processing and in blow molding, conditions in which a narrow MWD could cause melt fracture. As a consequence of this need, different methods have been developed trying to achieve this property. One of those is the multi-step process based on the production of different molecular weight polymer fractions in single stages, sequentially forming macromolecules with different length on the catalyst particles.
The control of the molecular weight obtained in each step can be carried out according to different methods, for example by varying the polymerization conditions or the catalyst system in each step, or by using a molecular weight regulator. Regulation with hydrogen is the preferred method either working in solution or in gas phase.
A problem typically associated with the processes of this type is that the different polymerization conditions used in the two steps can lead to the production of not sufficiently homogenous products, especially in cases of very broad molecular weight distributions. It is in fact difficult to obtain products having a high F/E ratio, for example higher than 100, which when subjected to a transformation process, yield products with a low number of unmelt particles (gels). In order to solve or minimize this problem it would be important to have a catalyst capable of producing broad MWD polymers also in a single polymerization step. This would allow, in case still broader MWD is desired, the use of less different polymerization conditions in the sequential polymerization process that would finally result in a more homogeneous product.
EP-A-119963 discloses catalyst components obtained by the reaction between a titanium halide and MgCl
2
-based carriers, containing from 1.5 to 20% of residual —OH groups, which are obtained by spray-drying MgCl
2
.EtOH solutions. The weight reaction ratio between the titanium halide and the MgCl
2
of the carrier has to be kept within the 0.001 to 2 range. The catalysts obtained however, are not able to give broad MWD since the shear sensitivity of the polymers (which is the ratio between the melt indices measured at weight of 20 kg and 2.16 kg at 190° C.) is about 25 (examples 4-5 and 8-9) although the polymerization process comprises two polymerization step under different conditions.
Moreover, the catalysts disclosed in this patent application are always used in a suspension polymerization process, while nothing is said about gas-phase polymerization. This latter kind of process is nowadays highly preferred due to both the high qualities of the products obtained and to the low operative costs involved with it. It would therefore be advisable to have a catalyst capable to produce broad MWD polymers and having at the same time the necessary features allowing its use in the gas-phase polymerization processes.
In EP-A-601525 are disclosed catalysts that, in some cases are able to give ethylene polymers with broad MWD (F/E ratios of 120 are reported). Such catalysts, obtained by a reaction between a Ti compound and a MgCl
2
.EtOH adduct which has been subject to both physical and chemical dealcoholation, are characterized by a total porosity (mercury method) higher than 0.5 cm
3
/g, a surface area (BET method) lower than 70 m
2
/g. The pore distribution is also specific; in particular in all the catalysts specifically disclosed at least 50% of the porosity is due to pores with radius higher than 0.125 &mgr;. Although the width of MWD is in some cases of interest, the bulk density of the polymers obtained is relatively low and this is probably due to non completely regular shape of the polymer formed which is in turn caused by non-proper behavior of the catalyst during polymerization. Hence, it is still very important to have a solid catalyst component capable of good performances in the gas-phase polymerization process (in particular capable of producing high bulk density polymer) and at the same time capable of giving polymers with a very broad MWD.
It has now surprisingly been found a catalyst component which satisfies the above-mentioned needs and that is characterized by comprising Ti, Mg, Cl, and by the following properties:
surface area, determined by BET method, of lower than 100 m
2
/g,
a total porosity, measured by the mercury method, of higher than 0.25 cm
3
/g
a pore radius distribution such that at least 45% of the total porosity is due to pores with radius up to 0.1 &mgr;m.
Preferably the catalyst component of the invention comprises a Ti compound having at least one Ti-halogen bond supported on magnesium chloride in active form. The catalyst component may also contain groups different from halogen, in any case in amounts lower than 0.5 mole for each mole of titanium and preferably lower than 0.3.
The total porosity is generally comprised between 0.35 and 1.2 cm
3
/g, in particular between 0.38 and 0.9.
The porosity due to pores with radius up to 1 &mgr;m is generally comprised between 0.3 and 1 cm
3
/g in particular between 0.34 and 0.8. In general terms the value of the porosity due to pores with radius higher than 1 &mgr;m is rather limited with respect to the total porosity value. Normally this value is lower than 25% and in particular lower than 15% of the total porosity. The surface area measured by the BET method is preferably lower than 80 and in particular comprised between 30 and 70 m
2
/g. The porosity measured by the BET method is generally comprised between 0.1 and 0.5, preferably from 0.15 to 0.4 cm
3
/g.
As mentioned above the catalyst of the invention show a particular pore radius distribution such that at least 45% of the total porosity is due to pores with radius up to 0.1 &mgr;m. Preferably, more than 50%, and in particular more than 65% of the total porosity is due to pores with radius up to 0.1 &mgr;m. If only the porosity due to pores with radius up to 1 &mgr;m is taken into account, the value of the porosity due to pores with radius up to 0.1 &mgr;m is even higher, generally more than 60%, preferably more than 70% and particularly more than 80%.
This particular pore size distribution is also reflected in the average pore radius value. In the catalyst component of the invention the average pore radius value, for porosity due to pores up to 1 &mgr;m, is lower than 900, preferably lower than 800 and still more preferably lower than 700. The particles of solid component have substantially spherical morphology and average diameter comprised between 5 and 150 &mgr;m. As particles having substantially spherical morphology, those are meant wherein the ratio between the greater axis and the smaller axis is equal to or lower than 1.5 and preferably lower than 1.3.
Magnesium chloride in the active form is characterized by X-ray s
Brita Diego
Sacchetti Mario
Basell Polyolefine GmbH
Choi Ling-Siu
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