0-TiCla catalyst systems

Type (a) behavior is shown by many first generation catalyst systems, e.g., a-TiCla, VCI3, etc., when used with dialkylaluminum halides as co-... 

Fig. 8a. Comparison of decaying and relatively stable catalyst systems. Polymerization at 80°C with TiCla in mixed undeoanes. No Ha.

The coordination environment around titanium in TiCla (in the solid-state) is six, i.e., each titanium is surrounded by six chlorines. The chlorines are involved as intermolecular bridging ligands between adjacent titanium centers. It is important to realize that this is the solid-state structure and the catalyst system is heterogeneous. Accordingly, only the surface sites will be active and bulk of the material will be not accessible to the reaction. It is reasonable to propose that at the surface several titanium cen-... 

In the 1970s, Solvay introduced an advanced TiCla catalyst with high activity and stereoregularity (271). The level of atactic polymer was sufficiently low so that its removal from the product was not required. When this catalyst was used in liquid monomer processes, residues were sufficiently reduced so that simplified systems for post-reactor treatment were acceptable. Montedison and Mitsui Petrochemical introduced MgCl2-supported high yield catalysts in 1975 (272). Use of these catalyst systems reduced the level of corrosive catalyst residues to the extent that neutralization or removal from the polymer was not required. Stereospecificity, however, was insufficient to eliminate the requirement for removal of the atactic polymer fraction. These catalysts were used in the Montedison high yield slurry process, which does not contain the sections required for alcohol treatment, neutralization, and diluent purification in older slurry processes (265). 

Synthesis The early polypropylene plants used a slurry process adopted from polyethylene technology. An inert liquid hydrocarbon diluent, such as hexane, was stirred in an autoclave at temperatures and pressures sufficient to keep 10 to 20 percent of the propylene monomer concentrated in the liquid phase. The traditional catalyst system was the crystalline, violet form of TiCla and AlCl (C2Hs)2- Isotactic polymer particles... 

Table 9). At a molar ratio of Al Ti = 300, the polymerizatiort activity of the fluorinated catalyst Cp TiFa was found to be about 50 times higher than that of the chlorinated system Cp TiCla. The higher activities of the... 

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