PERVAPORATIVE BUTANOL FERMENTATION BY CLOSTRIDIUM-ACETOBUTYLICUM B18

Extractive acetone-butanol-ethanol (ABE) fermentation was carried out successfully using pervaporation and a low-acid-producing Clostridium acetobutylicum B18. A pervaporation module with 0.17 m(2) of surface a rea was made of silicone membrane of 240 mu m thickness. Pervaporation experiments using make-up solutions showed that butanol and acetone f luxes increased linearly with their concentrations in the aqueous phas e. Fickian diffusion coefficients were constants for fixed air flow ra tes, and increased at higher sweep air flow rates. During batch and fe d-batch fermentations, pervaporation at an air flow rate of 8 L/min re moved butanol and acetone efficiently. Butanol concentration was maint ained below 4.5 g/L even though Clostridium acetobutylicum B18 produce d butanol steadily. Pervaporation could not remove organic acids effic iently, but organic acids did not accumulate because strain B18 produc ed little organic acid and recycled added organic acids efficiently. W ith pervaporation, glucose consumption rate increased compared to with out pervaporation, and up to 160 g/L of glucose was consumed during 80 h. Cell growth was not inhibited by possible salt accumulation or oxy gen diffusion through the silicone tubing. The culture volume was main tained relatively constant during fed-batch operation because of an of fsetting effect of water and product removal by pervaporation and addi tion of nutrient supplements. (C) 1994 John Wiley & Sons, Inc.