How para-xylene is made

Para-xylene is the chemical backbone of polyester bottles. About 37 million tons were wanted in 2014.

stations: 5
things upstream: 5
raw sources: 3
steps from the ground: 3

The short version

Para-xylene is produced by catalytic reforming of petroleum naphtha, which creates a mix of benzene, toluene and xylene isomers. Plants then separate para-xylene from its look-alikes by distillation, adsorption or crystallization. Nearly all of it goes on to become terephthalic acid for polyester and PET.

Reform the naphtha

Catalytic reforming turns naphtha into a stream rich in aromatic compounds. This stream is called reformate.

Goes in
Naphtha
Extract the BTX group

Benzene, toluene and the xylene isomers are pulled out of the reformate together. The three xylenes boil so close to each other that plain distillation cannot finish the job.
Isolate the para isomer

A series of distillation, adsorption or crystallization steps separates para-xylene from ortho and meta. These separations are major cost factors in the process.
Convert the leftover isomers

Isomers that are not para-xylene are reacted over catalysts to make more of it, and sent back through the separation. The loop wastes little.
Ship to polyester plants

Para-xylene is stored and sent to plants that turn it into terephthalic acid. That acid is the raw material for polyester and PET.

End of the linePara-xylene Next it goes into pet plastic, kevlar.

Worth repeating

Annual demand for para-xylene was estimated at 37 million tons in 2014 and still rising.
It is one of three xylene isomers that differ only in where two methyl groups sit on the ring.
Para-xylene is also the starting point for parylene, a plastic used as a thin protective coating.