Shell higher olefin process
The Shell higher olefin process is a chemical process for the production of linear alpha olefins via ethylene oligomerization and olefin metathesis invented and exploited by Royal Dutch Shell. The olefin products are converted to fatty aldehydes and then to fatty alcohols, which are precursors plasticizers and detergents. The annual global production of olefines through this method is over one million tonnes. A new production facility (capacity 200.000 tonnes) is planned in Qatar.
The process was discovered by chemists at Shell Development Emeryville in 1968. At the time ecological considerations demanded the replacement of branched fatty alcohols used widely in detergents, by linear fatty alcohols because the biodegradation of the branched compounds was slow, causing foaming of surface water. At the same time new gas oil crackers were being commissioned and ethylene supply was outpacing demand. The process was commercialized in 1977 by Royal Dutch Shell and following an expansion of the Geismar, Louisiana (USA) plant in 2002 global annual production capacity was 1.2 million tons.
Ethylene reacts by the catalyst to give longer chains. Unlike the Ziegler-Natta process, which aims to produce very long polymers, the oligomer stops growing after addition of 1-10 repeating units of ethylene. The fraction containing C12 to C18 olefins (40-50%) has direct commercial value in detergent production and is removed. For the remaining fraction to be of commercial interest two additional steps are required. The first step is liquid-phase isomerization using alkaline alumina catalyst leading to internal double bonds. For example, 1-octene is converted to 4-octene and 1-eicocene (a C20 hydrocarbon) is converted to 10-eicocene. In the second step olefin metathesis converts mixtures like these to 2-tetradecene which is a C14 component and again within commercial range.
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