Conference Dates

March 8-13, 2009


Acidogenic fermentation of biomass for the production of ethanol and acetic, propionic, butyric and lactic acids is a promising technology, in the sense that germ free conditions are not required, very diversified, less pretreated and cheap biomass can be used, and the molecules produced and their esters are consumed on a large scale by industries. The product recovery, separation and concentration steps downstream of the biomass transformation remain, however, a major challenge for the industrial application of acidogenic fermentation which produces very dilute (concentrations of only a few percent) and complex aqueous solutions of acids and ethanol. A novel extraction - re-extraction process for the recovery of ethanol and acetic, propionic, butyric and lactic acids from acidogenic fermentation broths is presented which is based on the transfer of the acids and ethanol to a glycerol phase via an intermediate solvent phase. Tri-n-octylamine based solvents are chosen in the first, extraction step of the process for their preferential extraction of acids. In the second, re-extraction step, the acids are extracted from the intermediate solvent with glycerol, opening perspectives for the transformation of glycerol into short chain esters, directly using the acids recovered. The novel TOA-based extraction – glycerol-based re-extraction process is experimentally investigated. First, butyric acid aqueous model solutions are tested. Next, the behavior with real fermentation broths is studied. The extraction re-extraction performance is observed to depend strongly on the solvent and on the operating conditions. The influence of the most important process parameters, such as the pH, the temperature, the composition of the aqueous phase is measured. For the first extraction step (water/TOA system), the distribution coefficient of butyric acid is seen to increase significantly with decreasing pH of the aqueous solution. The pH after extraction is linearly related to the pH before extraction. Furthermore, the extraction efficiency is seen to increase with decreasing temperature. Inversely, for the second extraction step (TOA/glycerol system), the extraction efficiency is seen to increase with increasing temperature. The simultaneous presence of butyric and acetic acids is shown not to affect the extraction of the individual acids.