Abstract: Beta-methylthiopropionaldehyde is prepared by (I) condensing a gaseous feedstream comprising both acrolein and water, advantageously the off-gas resulting from the air oxidation of propylene (and after the acrylic acid content has been absorbed therefrom), to obtain an aqueous condensate containing a fraction of said acrolein and a gaseous acrolein effluent, (II) partially vaporizing said aqueous condensate whereby to obtain a gaseous phase comprising essentially all of said acrolein fraction and a liquid phase comprising essentially no acrolein, (III) recycling said gaseous phase into said gaseous feedstream to be condensed, and (IV) directly reacting said gaseous acrolein effluent with methylmercaptan.

Abstract: Beta-methylthiopropionaldehyde is prepared from methylmercaptan and an acrolein-containing gaseous mixture derived as an off-gas from the catalytic oxidation of propylene.

Abstract: Acrylic acid is separated from its solutions in tri-n-butyl phosphate by establishing from such a solution a vapor phase comprising substantially all of the acrylic acid and a portion of the solvent, at a temperature below the degradation point of the acrylic acid; next partially or totally condensing said vapor phase; and then distilling the acrylic acid from such condensation product, while maintaining an amount of acrylic acid at the base of the distillation column, and conducting the distillation under conditions such that neither solvent degradation nor acrylic acid crystallization results.