In-situ recovery of butanol during fermentation

Abstract

End product inhibition can be reduced by the in situ removal of inhibitory fermentation products as they form. Extractive fermentation, in which an immiscible organic solvent is added to the fermentor in order to extract inhibitory products, was applied to the acetone-butanol fermentation. Six solvents or solvent mixtures were tested in batch extractive fermentations: kerosene, 30 wt% tetradecanol in kerosene, 50 wt% dodecanol in kerosene, oleyl alcohol, 50 wt% oleyl alcohol in a decane fraction and 50 wt% oleyl alcohol in benzyl benzoate. The best results were obtained with oleyl alcohol or a mixture of oleyl alcohol and benzyl benzoate. In normal batch fermentation of Clostridium acetobutylicum, glucose consumption is limited to about 80 kg/m3 due to the accumulation of butanol in the broth. In extractive fermentation using oleyl alcohol or a mixture of oleyl alcohol and benzyl benzoate, over 100 kg/m3 of glucose can be fermented. Removal of butanol from the broth as it formed also increased the rate of butanol production. Maximum volumetric butanol productivity was increased by as much as 60% in extractive fermentation compared to batch fermentation. Butanol productivities obtained in extractive fermentation compare favorably with other in situ product removal fermentations.