xylenes

Xylenes are a group of three isomeric dimethylbenzenes: o-xylene (1,2-dimethylbenzene), m-xylene (1,3-dimethylbenzene), and p-xylene (1,4-dimethylbenzene). Collectively they are known as xylenes, or mixed xylenes when produced as a combined stream. They are colorless liquids with a characteristic aromatic odor, relatively nonpolar, immiscible with water, and soluble in many organic solvents.

Commercially, xylenes occur in crude oil and coal tar, and are produced on a large scale from fossil fuels. Distillations yield mixed xylenes, which can be enriched to individual isomers by separation techniques such as crystallization, selective adsorption, or fractional distillation.

The major industrial uses relate to the conversion of each isomer to value-added products. p-Xylene is the principal precursor to terephthalic acid, a building block for polyethylene terephthalate (PET) plastics and related resins. o-Xylene is primarily oxidized to phthalic anhydride, used in plasticizers, coatings, resins, and some dyes. m-Xylene is converted to trimellitic anhydride, used in specialty polyesters and plastics. Mixed xylene streams are also widely used as solvents in paints, coatings, and printing inks.

Safety and handling: Xylenes are flammable and can be toxic if inhaled or absorbed through the skin; exposure may affect the nervous system, eyes, and respiratory tract. They should be handled with adequate ventilation, kept away from ignition sources, and stored in sealed containers. Environmental releases should be minimized.