Selection of organic solvents for in situ extraction of ethanol from fermentations with Clostridium thermohydrosulfuricum

Fifteen organic solvents were examined to determine their biocompatibility for in situ extraction of fermentation products from cultures of the thermophilic anaerobe Clostridium thermohydrosulfuricum. Five solvents (hexadecane, isooctane, kerosene, oleyl alcohol, Shellsol TD) were found to be non-toxic to Clostridium thermohydrosulfuricum. Interfacial tensions, phase separation and partition coefficients for ethanol of the biocompatible solvents were compared. With the exception of kerosene, these solvents showed good separation from the aqueous phase. Oleyl alcohol was found to have the highest partition coefficient for ethanol (K_D = 0.34 at 65°C). A continuous fermentation for 1200 hours showed no inhibition effects due to oleyl alcohol as extraction solvent.