Process for obtaining polyolefins

Details Process for obtaining polyolefins Process for obtaining polyolefins

2000-05-31

2002-05-14

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S160000, C526S127000, C526S129000, C526S943000, C502S152000, C502S117000, C502S120000, C502S121000, C502S122000, C502S123000, C502S155000

Reexamination Certificate

active

06388029

ABSTRACT:

The metallocene catalsts in combination with aluminium alkyls are scarcely active for the polymerization of olefins (U.S. Pat. No. 2,827,446). The controlled addition of small quantities of water to the polymerization medium remarkably increases the activity thus obtaining, sometimes, activities which are greatly higher than the ones obtained by using the known catalysts Ziegler-Natta (Makrom. Chem. 179, 2553 (1978) and 169, 163 (1973), DE 1022382, U.S. Pat. No. 3,184,416, U.S. Pat. No. 3,440,237). The controlled hydrolysis of alkyl aluminium leads to the obtainment of the corresponding aluminoxanes. When these aluminoxanes are used as activators of metallocene catalysts a very active catalytic system for the polymerization of olefins is obtained, particularly with zirconocene catalysts (U.S. Pat. No. 4,542,199).
On the other hand it was found out (EP 277004 and EP 426637) that the use of bulky boron compounds as co-catalysts enables high activities in the polymerization of &agr;-olefins too. The co-catalysts act by forming and stabilizing the active cations by means of non-coordinative anions, without preventing the incorporation of olefin during polymerization.
These catalytic systems are homogeneous catalysts soluble in the known solvents used in the polymerization of olefins and form very small polymer particles (<100 &mgr;m). Therefore, when these systems are used in gas phase or in suspension, a fouling or blocking of the reaction systems often takes place, thus forcing the stopping of the polymerization plant causing a loss in the production.
For these reasons, it is suitable to develop the heterogeneous catalysts which are able to keep the catalytic activity of the homogeneous systems and to control the dimensions and the morphology of the resulting polymer for the obtainment of particles greater than 100 &mgr;m and a high density of particles in the reactor (apparent density).
Works concerning the development of these catalytic solids have been carried out for many years. In general, the more used methods consist in the heterogeneization of the co-catalyst, the heterogeneization of the metallocene compound or in the heterogeneization of both components on an appropriate support.
The patent WO 91/09882 discloses the preparation of a supported catalytic system useful for the polymerization of olefins in suspension or in gas phase, which is formed by a homogeneous metallocene compound and an ionic non-coordinative co-catalyst of boron supported on an inorganic porous oxide. The support and the co-catalyst are physically joined, this fact can cause the migration to the reaction medium of the co-catalyst, thus obtaining products with a low apparent density and with a wide distribution of particle sizes. Moreover, the catalytic activity is very small. In a later patent (WO 93/11172) a method of lieterogeneization of said type of co-catalysts consisting in the functionalization of the boron co-catalyst bv means of two methods is disclosed. In one of them, the functionalization takes place with groups able to react with the free hydroxyl-groups of an inorganic support and, in the other method, functional groups are introduced in order to enable the later polymerization of the boron compound, creating an insoluble polymer in the reaction medium. Even though the chenmical anchorage of the co-catalyst assures that the active centers do not migrate in the reaction medium, these methods are chemically and economically expensive.
The patent EP 293 815 discloses the heterogeneization of metallocene catalysts supported on the inorganic oxides by the chemical reaction betwveen the functional alcoxysilane groups of the organometallic compounds and the surface hydroxyl groups of the inorganic oxides. The activity in the polymerization is not very high, probably as a consequence of the possible deactivation of the metallocene for the secondary products, which are formed during the reaction with the support.
The patent DE 3 840 772 A1 discloses the preparation of metallocene catalysts supported by reaction, between poly(methylhydrogensiloxane) and functionalized metallocenes with vinylic groups in the presence of a platinum catalyst. The process of synthesis and further anchorage of this kind of metallocene compounds are economically very expensive and the purity degree of tlhe supported metallocene is not the desired one resulting in very low polymerization activities.
The patents U.S. Pat. No. 4,659,685, EP 318 048, U.S. Pat. No. 50,302,562, EP 260 130 and EP 447 070 disclose the preparation of heterogeneous catalysts by directy supporting a non-metallocene compound of the metals of the groups 4, 5, or 6 of the periodic table on magnesium chloride, silica or aluminium phosphate, generally titanium halides, and a metallocene compound. The catalytic system is activated by the subsequent addition of aluminoxane or its mixtures with alkyl aluminium. The different polymerization rate of the titanium halides and of the metallocene compounds form multimodal polyolefins, by preventing the obtainment of polymers with a narrow and controlled polydispersity.
The patent EP 474 391 A2 and the studies of K. Soga (Macromol. Chem. Rapid Commun. 12, 367 (1991)) and of S. Collins (Macromoleculas 25, 1780 (1992) disclose the preparation of heterogeneous metallocene catalysts by supporting them onto inorganic porous oxides, magnesium halides or their mnxtures, previously treated with organoaluiminium compounds. The thus obtained catalysts are used in the polymerization of olefins in gas phase or in suspension and are activated with organoaluminium compounds. The resulting activities are very low and the obtained copolymers do not show a random distribution of the comonomer, thus developing two melting peaks. On the other hand, the metallocene compound cannot remain perfectly anchored because a migration in the polymerization medium may occur, with the relative obtainment of small particles.
The patent EP 628 566 and K. Soga in a study published in Makrom. Chem. Phys. 195, 3347 (1994) disclose the direct synthesis of metallocene catalysts on an inorganic support. The method consists in the chemical reaction between alkaline cyclopentadienyl cations and the functional groups of the support, the subsequent reaction of the resulting solid with halides of transition metals of groups 4, 5, or 6, allows the formation “in situ” of the metallocene onto the support. The resulting activities in polymterization are very low; this is probably due to the by-products of the synthesis reaction whose separation from the catalyst is difficult.
On the other hand, there are no clear evidences of the fact that for this process it is possible to synthesize directly and in a good yield, the organometallic complexes onto the supports.
The patents U.S. Pat. No. 5,057,475, EP 206 794 A1 and U.S. Pat. No. 4,701,432 A1 disclose a method for the preparation of supported metallocene aluminoxane catalytic systems, by means of the simultaneous or subsequent addition of a metallocene compound and an aluminoxane onto an appropriate support. These catalysts can be used in polymerizations with or without additional co-catalyst. But for some kind of uses, the produced polymers have molecular weights and incorporation of co-monomer below the desired level. Moreover, the absence of appropriate interactions between the catalytic components and the support could cause the migration of the organometallic compounds during polymerization.
The patents U.S. Pat. No. 4,939,217 and U.S. Pat. No. 5,064,797 disclose the preparation of a supported aluminoxane by means of bubbling of a moistened inert gas in a solution of alklyl aluminium in the presence of the support. When a solution of metallocene is added, a heterogeneous catalytic system with good activities in the polymerization of olefins is obtained. But the thus obtained aluminoxane particles could not remain completely anchored onto the inorganic support because neither the morphology, nor the distribution and the size of the particle are the desired ones for this kind of uses. Consequently th

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