Reactive extraction of propionic acid using tri-n-octylamine, tri-n-butyl phosphate and aliquat 336 in sunflower oil as diluent

BACKGROUND: Propionic acid is widely used in chemical and allied industries and can be produced by biocultivation in a clean and environmentally friendly route. Recovery of the acid from the dilute stream from the bioreactor is an economic problem. Reactive extraction is a promising method of recovering the acid but suffers from toxicity problems of the solvent employed. There is thus a need for a non-toxic solvent or a combination of less toxic extractants in a non-toxic diluent that can recover acid efficiently. RESULTS: The effect of different extractants (tri-n-butylphosphate (TBP), tri-n-octylamine (TOA) and Aliquat 336) and their mixed binary solutions in sunflower oil diluent was studied to find the best extractant-sunflower oil combination. Equilibrium complexation constant, K-E, values of 4.02, 3.13 and 1.87 m(3) kmol(-1) were obtained for propionic acid extraction using Aliquat 336, TOA and TBP, respectively, in sunflower oil. The effect of different modifiers (1-decanol, methylisobutyl ketone, butyl acetate and dodecanol) on the extraction was also studied and it was found that modifiers enhance extraction, with 1-decanol found to be the best. CONCLUSION: The problem of toxicity in reactive extraction can be reduced by using a non-toxic diluent (sunflower oil) or a modifier in a non-toxic solvent, with the extractant. The addition of modifiers was found to improve the extraction. (c) 2008 Society of Chemical Industry