Patent GB-689411-A (GB)
Title: Concentration of organic acids
IPC: C07C51/48
Filed: 1950-12-15
Abstract: Fatty acids containing up to 4 carbon atoms are extracted from their aqueous solutions by a mixture of a trialkyl phosphate and a hydrophobic diluent which forms an azeotropic mixture with water of lower boiling-point than that of the acids, the diluent, or water or any other azeotropic mixture formed by two or more of these substances.  The extract may then be distilled to remove first the diluent/water azeotrope and then the fatty acids (see Group III). The invention may be used to recover the acids produced by the fermentation process of Specification 689,412. The extraction may be performed on a batch or in a continuous manner with concurrent or countercurrent flow of the two phases. In examples: (1), (2) and (4) propionic acid is extracted from its aqueous solution by a mixture of tributyl phosphate and benzene or ethylene chloride; (3) molasses fermented with propionbacterium arabinosum is acidified to pH4 with sulphuric acid and extracted with a mixture of tributyl phosphate and benzene.  The extract is distilled to obtain a mixture of acetic, propionic and butyric acids.ALSO:Fatty acids containing up to 4 carbon atoms are extracted from their aqueous solutions by a mixture of a trialkyl phosphate and a hydrophobe diluent which forms an azeotropic mixture with water of lower boiling point than that of the acids, the diluent, or water or any other azeotropic mixture formed by two or more of these substances.  The extracts are then distilled to remove first the diluent/water azeotrope and then the fatty acids. The invention may be used to recover the acids produced by the fermentation process of Specification 689,412, [Group IV (b)]. Specified trialkyl phosphates are tripropyl-, tributyl, tri-(butoxy-ethyl), tri-(2-ethylhexyl)-, and tri-(chlor-ethyl)-phos-(2-ethylhexyl)-, and tri(chlor-ethyl)-phosphates.  Specified hydrophobe diluents are benzene, toluene, cyclohexane, methylene chloride, trichloroethylene and 1.2-dichloroethane.  Some of the diluent may be added to the extract after the extraction process and before or after distillation has commenced.  Distillation is preferably effected at below 150 DEG C at sub-atmospheric pressures to minimize hydrolysis of the trialkyl phosphate.  If a strong acid is present in the extract a basic substances e.g. sodium citrate, bicarbonate or acetate or dibasic sodium phosphate is added thereto before the distillation.  In examples (2) propionic acid is extracted from its aqueous solution with a mixture of tributyl phosphate and benzene and the extract distilled first at atmospheric pressure to remove the benzene/water azeotrope and then at 35-43 mm. of mercury to remove the propionic acid; (3) molasses fermented with propionibacterium arabinosum is acidified to pH4 with sulphuric acid and extracted with a mixture of tributyl phosphate and benzene.  The extract is agitated with dibasic sodium phosphate, distilled at atmospheric pressure to remove the water/benzene azeotrope and a mixture of acetic, propionic and butyric acids is then flashed off by reducing the pressure to 35 mm. while continuing the heating.