Paraxylene

Para-xylene, or p-xylene, is an aromatic hydrocarbon with the chemical formula C8H10. It is one of the three isomers of xylene, characterized by two methyl groups attached to opposite positions on the benzene ring. At room temperature it is a colorless, flammable liquid with a sweet odor. Its boiling point is about 138.7°C and its melting point is around -47°C; it is only sparingly soluble in water and miscible with many organic solvents.

Production and separation of p-xylene occur in the petrochemical industry as part of the C8 aromatics stream generated during catalytic reforming of naphtha and related processes. In mixed xylene streams, para-, meta-, and ortho-xylene are present; separation and purification are achieved by fractional distillation, selective crystallization, or adsorption techniques using zeolites or similar materials to yield high-purity p-xylene for downstream use.

Most of the world’s p-xylene is converted to terephthalic acid (TPA) or its dimethyl ester (DMT) via oxidation or esterification, respectively. TPA and DMT are precursors to polyethylene terephthalate (PET), the polymer widely used for beverage bottles, fibers, and film. Additional applications include use as a solvent or as an intermediate in chemical syntheses, though the bulk of production centers on forming PET-related products.

Safety and handling notes: p-Xylene is flammable and should be stored away from heat and ignition sources. Vapors can form explosive mixtures with air; appropriate ventilation and containment measures are required. Exposure should be minimized according to regulatory guidelines. Environmental releases should be managed to prevent soil and water contamination.