Process for Recovering Aliphatic Monocarboxylic Acids from Distillation Residues

A process is provided for recovering aliphatic monocarboxylic acids having from 4 to 11 carbon atoms from the distillation residue obtained in the oxidation of the corresponding aldehyde by means of oxygen or oxygen-containing gas mixtures in the presence of alkali metal carboxylates or alkaline earth metal carboxylates to form the corresponding monocarboxylic acid and subsequent distillation, characterized in that the distillation residue is reacted with an aqueous acid in a tube reactor and the two-phase mixture flowing out from the tube reactor is introduced into a settling vessel in which the organic phase which separates out has a pH of 4.5 or less.