Cracking of oil products

The distillation of crude oil results in several fractions, with the naphtha (C5 - C10 hydrocarbons) and gas oil (C14 - C20) fractions together making up as much as half the output. Demand for these hydrocarbons is exceeded, and so these fractions are cracked - which literally means breaking the larger molecules into smaller ones. Crude oil will usually contain dissolved ethane and propane too, and these are removed before distillation and used as feedstock for cracking.

One of the products of cracking is raw pyrolysis gasoline (RPG), which is rich in benzene and other aromatic compounds. Click here for more on this process.

Reforming of naphtha

The reforming of naphtha is exactly that Ð the molecules in naphtha, mainly straight chain alkanes in the C5 to C10 range, are re-formed into molecules with the same number of carbon atoms but different structures.

Naphtha vapour and hydrogen are passed over a platinum/alumina catalyst, and is converted into a variety of products, including benzene and other aromatics, which can be separated from each other. One of the main purposes of catalytic reforming of naphtha is raising the octane rating of petrol. For more information, click here.

Disproportionation of methylbenzene

Naphtha reforming generates methylbenzene (toluene) among the aromatic products, but unfortunately the demand for this is much lower than for dimethylbenzene (xylene), produced in much smaller quantities by reforming.

Methylbenzene can, however, be converted to dimethylbenzene and benzene using a catalyst. The benzene can then be separated from the mixture. To find out more, click here.