Patent ID: 7728184

Claim:
An improved process for the production and purification of vinyl-aromatic monomers which comprises: a) feeding a stream consisting of an aromatic hydrocarbon together with a stream essentially consisting of a C 2 -C 3 olefin to an alkylation section; b) feeding the reaction product coming from the alkylation section to a first separation section; c) discharging from the first separation section a first stream consisting of non-reacted aromatic hydrocarbon, which is recycled to the alkylation section, a second stream essentially consisting of a mono-alkylated aromatic hydrocarbon, a third stream essentially consisting of dialkylated aromatic hydrocarbons, sent to a transalkylation section, and a fourth stream essentially consisting of a mixture of polyalkylated aromatic hydrocarbons; d) feeding the second stream of step (c) to a dehydrogenation section; e) feeding the reaction product coming from the dehydrogenation section to a second separation/purification section, comprising at least one distillation column; and f) discharging a stream consisting of the vinyl-aromatic monomer with a purity of over 99.7% by weight, from the head of said at least one distillation column, wherein: after a first cooling with heat recovery, the gas leaving the dehydrogenation step, after washing with sprayed water, is fed and condensed in the shell of a tube bundle heat exchanger maintained vertical or horizontal, in whose tubes a cooling fluid flows; the gas feeding is effected from the lower part of the exchanger with the liquid deriving from the condensation which refluxes and leaves the exchanger, either totally or partially, still from the lower part of the shell and is sent to the second separation/purification section (e); and the possible gas and non-condensed substances leave the shell from the upper part of the exchanger.