Also known as: butene, C4
In a refinery, butylene is important as a feed stock to the alky unit to make C4 Alkylate, the highest-value alkylate. Butylene is also used to make MTBE and IsoOctene, which are both high-quality gasoline blend stocks.
Refinery butylene primarily comes from the FCC unit. Small amounts of butylene are also produced by other cracking units, such as the , but these less likely to be separated for use in the alky. Butylene can also be sourced externally from steam crackers, which produce a large amount of butylene when processing light naphtha as a feed stock.