|In the 1960s synthetic zeolites started to replace silica/alumina
catalysts. A big advantage of zeolites is that they are more selective,
giving a higher yield of products in the more useful C5 to C10 range,
and fewer in the C3 to C4 range. They also give more branched molecules
which makes for a higher octane petrol
The oil industry switched to zeolites almost overnight and still uses
them. The combination of higher activity and improved selectivity saves
vast amounts of energy and money, making cheaper products possible.
The greater effectiveness of catalytic cracking with zeolites rather
than silica-alumina saved over 200 million barrels of crude oil in 1977
in the USA alone, about 30 million tonnes.
Over 400 fluid catalytic cracking units are in operation at oil refineries
around the world today. The reactions are varied. They include: