Asian Chemical Connections
Aromatics are a major group of unsaturated cyclic hydrocarbons containing one or more rings. These are typified by benzene which is the simplest aromatic hydrocarbon with a 6-carbon ring containing three alternating double bonds. The term ‘aromatics’ is derived from the compounds initially discovered which had fragrant odours.
In the petrochemical industry, the aromatic hydrocarbons of commercial interest include benzene, toluene, orthoxylene and paraxylene. They are derived from the pyrolysis gasoline produced during the steam cracking of liquid hydrocarbons such as naphtha, gas oil and condensates, or from the catalytic reforming of naphtha in an oil refinery. A small amount is still produced from the distillation of light oils produced during the manufacture of coke.
These aromatic compounds are used to produce a number of petrochemical intermediates including styrene, phenol, purified terephthalic acid (PTA) and phthalic anhydride (PA). A number of polymer families are also derived from these aromatics such as polystyrene (PS), polyester/polyethylene terephthalate (PET), polycarbonate, nylon and polyurethanes (PUs).
Benzene is the largest volume aromatic petrochemical used to produce a number of petrochemical intermediates such as ethylbenzene for styrene production, cumene for phenol and acetone, cyclohexane and nitrobenzene.
Toluene is used in solvent applications and is consumed in the manufacture of toluene diisocyanate (TDI) which is used in the manufacture of polyurethane foams. A major use of toluene is to make benzene and xylenes using a number of technologies.
Paraxylene is the largest volume isomer of the mixed xylenes. Around 98% of paraxylene demand comes from the polyester chain via one of its intermediates, purified terephthalic acid (PTA) or dimethyl terephthalate (DMT). These two products are reacted with ethylene glycol to make PET resins.
Orthoxylene is consumed mainly in the manufacture of phthalic anhydride, which is used to make phthalate plasticizers, unsaturated polyesters resins and alkyd resins.
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