Production of ethanol by continuous fermentation and liquid-liquid extraction

A continuous pilot plant was constructed for fermentation production of ethanol, using liquid-liquid extraction to remove the product and with recycle of the fermented broth raffinate. The plant was operated for up to 18 days with feed glucose concentrations in the range 10.0-45.8% (w/w). The solvent was n-dodecanol and immobilized yeast was used to overcome the problem of emulsification. The concentration of by-products in the fermented broth had no adverse effect on the rate of ethanol production. A mathematical model to predict the time required for achievement of 99% of the steady-state by-products concentrations was shown to be in good agreement with the experimentally determined concentration of the main by-product, glycerol. At a feed glucose concentration of 45.8% (w/w), the aqueous purge was equivalent to 2.8 m3 of effluent per m3 of ethanol produced and represented a 78% reduction in the volume of the aqueous purge compared with using a feed containing 10% (w/w) glucose.