(68f) Recovery of Chemicals Produced by Acidogenic Fermentation

The use of alternative and renewable resources, such as biomass, for the production of energy and chemicals is motivated by decreasing oil reserves and environmental concerns. Acidogenic fermentation of biomass for the production of ethanol and acetic, propionic, butyric and lactic acids offers major advantages in that it allows: (i) non germ free conditions; (ii) using very diversified, less pretreated and cheap biomass; (iii) producing molecules and corresponding esters consumed on a large scale by the industries.

The product recovery, separation and concentration steps downstream of the biomass transformation remain a major challenge for the application of acidogenic fermentation which produces very dilute (concentrations of only a few percent) and complex aqueous solutions of acids and ethanol. A number of separation processes can be potentially used, but a process which is technically, energetically and environmentally promising has not been developed yet. In this work, a novel extraction - re-extraction process is presented which is based on the transfer of the acids and ethanol to a glycerol phase via an intermediate solvent phase. In the first, extraction step, tri-n-octylamine based solvents are chosen for their preferential extraction of acids. In the second, re-extraction step, glycerol is used to extract the acids from the intermediate solvent. Glycerol being a by-product of the growing biodiesel production, its use opens perspectives for the transformation of glycerol into short chain esters, directly using the acids recovered.

The mass based distribution coefficients were experimentally measured. Both model solutions and real fermentation broths were used. Solutions were stirred to reach equilibrium and then centrifuged. The concentrations of butyric acid in the aqueous phase before and after extraction were determined by gas chromatography. The influence of the pH, the temperature and the composition of the aqueous phase on the recovery of the acids was studied. Furthermore, the influence of the composition of the organic phase, i.e. different modifiers and diluents, was investigated.

Acknowledgements

The authors would like to acknowledge the Belgian Fonds pour la formation à la Recherche dans l'Industrie et dans l'Agriculture (F.R.I.A.) for the financial support.

References

1. C. O'Driscoll (2007) Biofuels, Bioprod., Bioref., 1, 6?7