Oligomerization of light alkenes

The light alkenes (propene, butene and pentene) are important feedstocks for alkylation, oligomerization and the synthesis of ethers (refs. 1,2). MTBE (methyl tert-butyl ether) and TAME (tert-amyl methyl ether) have research octane numbers of 118 and 112 respectively. These premium blend stocks are synthesised by reaction of methanol with isobutene or isopentene (refs. 3,4). The reaction with methanol is selective towards the branched alkenes so that a mixture may be treated and the straight chain alkenes recovered for other processing such as alkylation. 

After the oligomerization reactor and the liquid-liquid separator, the organic product has to undergo an intensive product wash to make sure that no catalyst enters the distillation columns. In the following series of distillations, the technically desired 1-alkene cut Ce-Cig is separated and the too light C4 and the too heavy C18+ cuts are combined and isomerized to internal linear olefins in the isomerization reactor. These internal alkenes are then converted in the metathesis reactor to form internal alkenes. The desired C -Cig fraction is isolated, whereas the lights and the heavies are again recycled into the isomerization reaction. 

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