Styrene Production from Methanol & Toluene

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

* Alkylation. Initially, fresh and recycled toluene and methanol are vaporized, superheated, and fed to alkylation reactors. The reaction is carried out in a fixed-bed reactor at around 400 - 425 °C at atmospheric pressure in the presence of a modified zeolite catalyst. The effluent from the alkylation, containing Styrene, ethylbenzene, hydrogen, carbon monoxide and unconverted methanol and toluene, is then directed to separation steps downstream.

* Styrene separation. The effluent from the alkylation 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 distillation column, in which unconverted methanol and dissolved trace hydrocarbons are recovered. Water withdrawn from column bottom is discharged. The organic phase from the settling drum is directed to purification steps downstream.

* Purification. The organic phase from Styrene separation 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, unreacted toluene is separated from the Styrene stream and recycled to the alkylation reaction. In a subsequent distillation step, Styrene is separated from ethylbenzene, which is sold as by-product. Finally, Styrene is purified from residual impurities – mainly C9 aromatic compounds – in a last distillation step.