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.