GB788931A - Improvements in or relating to the separation of organic mixtures - Google Patents

Abstract

The components of a mixture of one or more aliphatic carboxylic acids, water and formaldehyde are separated by rectifying the mixture in a distillation column in the presence of an auxiliary organic liquid which is insoluble in water and, which forms with water and formaldehyde, but not with the acid or acids, an azeotropic mixture having a boiling-point below that of the acid or acids, recovering anhydrous acid or acids from the base of the column and separating formaldehyde as an aqueous solution from a heterogeneous liquid phase condensed from the vapour phase of the column. The auxiliary organic liquid may be di-isopropyl ether, di-butyl ether, isopropyl or butyl formates or acetates, methyl isopropyl ketone, or methyl isobutyl ketone, when the acids are formic acid and acetic acid. A mixture also containing a ketone having a boiling-point below that of the acid or acids, such as acetone, may also be separated using an auxiliary organic liquid incapable of forming a binary azeotrope with the ketone or a ternary azeotrope with the ketone and water, and the boiling-point of the azeotropic mixture which it forms with formaldehyde and water must be between that of the ketone and the acid or acids; examples are isopropyl formate and isopropyl acetate. The ketone may be removed with the aqueous formaldehyde solution, or, using fractional distillation, pure ketone vapour may be withdrawn at the top of the column, and the azeotropic mixture vapour lower down. In examples: (1) isopropyl ether is used in the separation of a mixture of acetic and formic acids, formaldehyde and water, and (2) isopropyl acetate is used with a mixture also containing acetone.