Supported Polypropylene Catalysts

Moore, E.P. The Rebirth of Polypropylene Supported Catalyst, Munich, Vienna, New York, Hanser/Gardner Publications, 1998. 

EP Moore, Jr. The Rebirth of Polypropylene Supported Catalysts, How the People of the Montedison Laboratories Revolutionized the PP Industry. Munich Hanser Publishers, 1998. 

Polymerization. Supported catalysts are used extensively in olefin polymerization, primarily to manufacture polyethylene and polypropylene. Because propylene can polymerize in a stereoregular manner to produce an isotactic, or crystalline, polymer as well as an atactic, or amorphous, polymer and ethylene caimot, there are large differences in the catalysts used to manufacture polyethylene and polypropylene (see Olefin polymers). 

Figure 3.16 Possible structures for active sites in heterogeneous Ziegler-Natta catalysts producing atactic polypropylene. Mt = Mg or Mn (MgCl2- or MnCl2-supported catalysts), or Ti (non-supported TiC f-based catalysts) inm-surface of MgCl2, MnCl2 or TiCl3...

The tacticities are also different, depending on whether the metallocene is supported. The homogeneous Me2C(CpFlu)ZrCl2/MAO catalyst gives a higher yield of syndiotactic polypropylene than the supported catalyst (Fig. 26). 

The dependence the polymer microstructure on the propylene concentration in the reactor is shown in Table XVI. By varying the monomer concentration in operation with the supported catalyst, one can obtain polypropylenes with relatively low concentration of rrrr pentads. At low propylene concentrations, it is possible that m insertions are formed by epimerization. The yield of these isolated m diads is significantly increased when the catalyst is supported. Similar effects were shown by catalysts producing isotactic polymer. 

Application To produce polypropylene (PP) homopolymer, random copolymer and impact copolymer using the BP Innovene gas-phase process with proprietary 4th generation supported catalyst. 

The differences in the properties of polypropylene obtained with homogeneous and supported catalysts are also illustrated by their 13C-NMR spectra (Fig. 8). The spectrum of the polymer formed by C-l is identical to that of isotactic polypropylene (Fig. 8a), whereas the spectra of the polymers produced by supported catalysts (Fig. 8b,c) are typical of the polypropylene in which isotactic domains alternate with many stereodefects [41]. 

On the ground of these contrasting results it is felt that the role of the donor needs more in depth studies. With regard to the role of the support, the MgCl2-based catalysts permit to narrow the polypropylene MWD. In fact, the non-supported catalysts produce polymers having Klw/Mn in the range 6-10 53). 

While the passage from the discovery of the supported catalysts to their industrial use was quite rapid for polyethylene, it was much slower for polypropylene because... 

The first MgCL,-supported catalyst for polypropylene, was developed by Montedison in cooperation with Mitsui Petrochemical. In 1978 it was carried over to an already existing plant for the polymerization in a slurry. Thus, in comparison to the preexisting situation (Fig. 48), it was possible to achieve the first step toward eli-... 

Supported metallocene catalyst systems are preferred to soluble versions in conventional polyolefin plants, which were designed to use supported Ziegler-Natta or Cr203-based catalysts. Metallocenes can be supported on a number of substrates, such as Si02, MgC or AI2O3. Supported catalysts also provide polypropylene with fewer stereochemical defects. 

Gas phase polymerizations, using other supported catalysts, are also employed to make isotactic polypropylene, with productivities of the same order as those reported for polyethylene manufacture. 

Most recently, a further family of MgCl2-supported catalysts has been developed in which the internal donor is a succinate rather than a phthalate ester. As is the case with the phthalate-based catalysts, an alkoxysilane is used as external donor. The essential difference between these catalysts is that the succinate-based systems produce polypropylene having much broader molecular weight distribution, discussed below in the section entitled Catalyst/Polymer Relationship. ... 

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