CONTINUOUS FERMENTATION WITH PRODUCT RECOVERY BY IN-SITU EXTRACTION

The productivity of fermentations is often limited by end product inhi bition. This can be avoided by continuous removal of the inhibiting pr oduct from the broth. Such in-situ separation can be conveniently acco mplished by liquid-liquid extraction. As an example, the continuous fe rmentation of ethanol by the thermophilic, anaerobic bacterium Clostri dium thermohydrosulfuricum is investigated in a 20-1 fermenter with si multaneous in-situ extraction by oleyl alcohol as organic solvent. Con tinuous fermentations with and without in-situ extraction were carried out with systematic variation of the independent operating conditions , viz. feed glucose concentration, broth flow rate and solvent flow ra te. The experimental results of 18 steady states are reported. They sh ow that in-situ extraction doubles the yield, selectivity and space-ti me yield of ethanol in comparison to fermentations without in-situ ext raction. A biomodel elucidates the influence of feed glucose concentra tion, broth flow rate and solvent flow rate on the productivity of the fermentation process. Finally, a cost model was developed for the inv estigated fermentation which allows economic evaluation of the results of experiments and simulation. A sensitivity study elucidates the eco nomic limits and advantages of fermentation with in-situ extraction co mpared to a common fermentation without product separation.