Process for the production of vinyl-aromatic monomers which comprises: a) feeding an aromatic stream and an olefinic stream to alkylation; b) feeding the reaction product coming from the alkylation section to a first separation section; c) recovering the mono-alkylated aromatic hydrocarbon from the first separation section; d) feeding the mono-alkylated aromatic product to a dehydrogenation section; e) cooling and condensing the reaction gases in the shell of one or more heat exchangers; f) feeding the reaction product coming from the dehydrogenation section to a second separation section; g) recovering the stream of vinyl-aromatic monomer.