PX(para-xylene)

P-Xylene (para-xylene) is an aromatic hydrocarbon. It is one of the three isomers of dimethylbenzene known collectively as xylenes. The p- stands for para-, indicating that the two methyl groups in p-xylene occupy the diametrically opposite substituent positions 1 and 4.

p-Xylene is produced by catalytic reforming of petroleum naphtha as part of the BTX aromatics (benzene, toluene and the xylene isomers) extracted from the catalytic reformate. The p-xylene is then separated out in a series of distillation, adsorption or crystallization and reaction processes from the m-xylene, o-xylene, and ethylbenzene. Its melting point is the highest among this series of isomers, but simple crystallization does not allow easy purification due to the formation of eutectic mixtures.

p-Xylene is an important chemical feedstock. notably terephthalic acid (TPA), purified terephthalic acid (PTA) and dimethyl-terephthalate (DMT). TPA, PTA and DMT are used to manufacture polyethylene terephthalate (PET) polyesters, a kind of plastic.