Styrene Production from Ethylbenzene

The process under analysis comprises the following major sections: (1) dehydrogenation; (2) crude Styrene separation and (3) purification.

* Dehydrogenation. Initially, fresh and recycled ethylbenzene are vaporized, superheated, diluted in steam and fed to dehydrogenation reactors. The reaction is carried out over fixed bed catalysts in two radial-flow, adiabatic reactors operating in series. As the dehydrogenation reaction is endothermic, reaction heat is supplied by preheated steam that is mixed with ethylbenzene upstream the first reactor and by an inter-reactor reheater. The effluent from the dehydrogenation, containing Styrene, unreacted EB, toluene and benzene by-products and impurities is directed to separation steps downstream.

* Crude Styrene Separation. The effluent from the dehydrogenation step is cooled, partially condensed, and fed to a settling drum. Vapors are disengaged from the liquid phase, compressed, cooled and passed through an absorber/stripper system, for the recovery of residual aromatics which are recycled. The aqueous phase from the settling drum is fed to a steam stripper, in which dissolved trace hydrocarbons are recovered. The organic phase – a crude Styrene stream – is directed to purification steps downstream.

* Purification. The crude Styrene stream is mixed with dinitrophenols, which act as inhibitor to lessen polymer formation throughout distillation steps downstream, carried out under vacuum. In a first distillation step, a mixture of benzene and toluene by-products is separated from the Styrene stream. This mixture is further distilled for the separation of the by-products. In a subsequent distillation step, Styrene is separated from EB, recycled to the dehydrogenation. Finally, Styrene is purified from residual impurities – mainly C9 aromatic compounds – in a last distillation step.