petrochemical, any one of a large group of chemicals derived from a component of petroleum or natural gas. The cracking processes for manufacturing gasoline produce vast quantities of gaseous hydrocarbons. Originally considered waste products suitable only for use as illuminants and fuels, the gases today are manufactured into petrochemical substances widely employed in industry. Important petrochemical compounds are alcohols and aldehydes, butylene, butadiene, ethylene, propylene, toluene, styrene, acetylene, benzene, ethylene oxide, ethylene glycol, acrylonitrile, acetone, acetic acid, acetic anhydride, and ammonia. Materials made from the gases include carbon black, synthetic rubber, polystyrene, polypropylene, and polyethylene. Petrochemicals are widely used in agriculture, in the manufacture of plastics, synthetic fibers, and explosives, and in the aircraft and automobile industries.

Strictly, any of a large class of chemicals (as distinct from fuels) derived from petroleum and natural gas. The category has been broadened to include a much larger range of organic compounds and a few inorganic compounds (including carbon black, sulfur, and ammonia). Some materials cannot be classifed unequivocally because they have alternative sources (benzene from coal, ethanol from fermentation). Like crude oil and natural gas, most petrochemicals consist mainly of carbon and hydrogen and are called hydrocarbons. Petrochemicals used as raw materials (feedstocks) include ethylene, propylene, butadiene, benzene, toluene, xylene, and naphthalene. Among the myriad petrochemical products are plastics (e.g., polyethylene, polypropylene, polystyrene), soaps and detergents, solvents, drugs, fertilizers, pesticides, explosives, synthetic fibres and rubberss, paints, epoxies, flooring and insulating materials, luggage, and recording disks and tapes.

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