The original source of toluene from coke-oven gas has been replaced by the catalytic reforming of naphthas and from pyrolysis gasoline co-produced in the steam cracking of liquid feeds. A very small amount is still produced from light oil formed by the carbonisation of coal while small quantities are recovered as a byproduct in styrene manufacture.
In the catalytic reforming route, a hydrocarbon mixture rich in aromatics is passed over a dehydrogenation catalyst at around 530oC and 17-21 bar. After removing light hydrocarbon gases by fractionation, the reformate is sent to a tower where an aromatic-rich fraction is obtained. Toluene can be recovered from the middle cut by azeotropic distillation, extractive distillation or solvent extraction with solvent extraction the route usually employed.
Pyrolysis gasoline produced by the steam cracking of liquid hydrocarbons such as naphtha and gas oil has become a growing source of toluene. The pygas must be hydrogenated prior to the aromatics extraction because of its instability.
A new process called Cyclar, which has been developed by BP and UOP, converts butanes and propanes in LPGs into aromatics. So far, only one commercial plant located in Saudi Arabia has been built.