Other refinery processes, instead of splitting molecules, rearrange them to add value. Alkylation makes petrol components by combining some of the gaseous byproducts of cracking. The process, which essentially is cracking in reverse, takes place in a series of large, horizontal vessels. Reforming uses heat, moderate pressure and catalysts to turn naphtha into high-octane petrol. To make petrol , refinery workers carefully blend together a variety of hydrocarbons.
Technicians also add performance additives and dyes that distinguish the various grades of fuel.
By the time the petrol is pumped into a car it contains more than 200 hydrocarbons and additives.