The present invention is a process for the production of styrene monomer from ethylbenzene comprising the steps of: a) catalytically dehydrogenating said ethylbenzene in the presence of steam thereby catalytically producing a dehydrogenation effluent gas containing essentially unreacted ethylbenzene, styrene monomer, hydrogen, steam and divinylbenzene; b) quenching said effluent gas with an aqueous reflux in at least a quenching column to cool said effluent gas, and thereby obtaining a gas at the overhead and in the bottom a liquid stream warmer than the aqueous reflux; c) condensing said overhead gas thereby producing a liquid organic phase, an aqueous phase and a gaseous phase; d) using a portion or the whole of said aqueous phase of step c) as reflux for said step b) of quenching; e) sending to a decanter the liquid stream obtained at step b) to recover an aqueous phase and an organic phase.