Disclosed are after-treatment processes and apparatus for synthesis plants, particularly urea and ammonium nitrate plants, but applicable also to various other plants in which the synthesis reaction does not go to substantial completion. In such plants product is fed to an evaporator for concentration and then to a solidification stage. The vaporous overhead stream from the evaporator contains entrained synthesis product, one or more unreacted starting materials, and solvent (usually H2 O). It is condensed, and the condensate is brought into mass and heat exchange relationship with the vaporous overhead stream from the evaporator substantially without material transfer of solvent to the condensate stream. The condensate stream is thereby enriched in synthesis product, heat is added to it, and unreacted starting material is desorbed from it. The product-enriched condensate is delivered to the solidification stage for processing there. Production capacity is increased and plant effluent is decreased or eliminated.