VAST process titanium

The advantages of shape selective catalysis are alreacfy ejq)loited in a number of industrial processes [11-14]. Astonishingly, virtually all these processes rely on a single structural type of catalyst, viz. zeolite ZSM-5 in various modifications, or its titanium containing analogue TS-1 [15]. It is, moreover, noteworthy that many of these processes convert and/or produce mononuclear aromatic compounds. It is not surprising, therefore, that a vast scientific literature exists on shape selective reactions of benzene derivatives in zeolite ZSM-5. 

The chief mined ore of titanium is ilmenite (iron titanium oxide, FeTiC>3) and it occurs as vast deposits of sand in Western Australia, Canada and the Ukraine. Large deposits of rutile (titanium dioxide, TiO ) are known in North America, and South Africa. World production of the metal itself is around 90,000 tonnes per year, small compared to titanium dioxide production which is 4.3 million tonnes per year. Reserves of titanium amount to more than 600 million tonnes and while there is an abundance of this element it is extremely costly because it has to be extracted by a complicated process, and yet it could be so much more useful if it was cheaply available. 

In this case, the aluminum alkyl is functioning as a cocatalyst, sometimes also called an "activator." Titanium alkyls, believed to be active centers for polymerization, are created through transfer of an alkyl from aluminum to titanium, known as "alkylation." Molar ratios of cocatalyst to transition metal (Al/Ti) are typically 30 for commercial polyethylene processes using Ziegler-Natta catalysts (lower ratios are used for polypropylene). The vast majority of aluminum alkyls sold into the polyethylene industry today is for use as cocatalysts. With TEAL, the most widely used cocatalyst, alkylation proceeds as in eq 4.8 ... 

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