SIMULTANEOUS FERMENTATION AND SEPARATION IN THE ETHANOL AND ABE FERMENTATION

Simultaneous separation of solvent products during fermentation reduce s product inhibition and increases reactor productivity. Separation te chniques used for simultaneous extraction during ethanol fermentation and butanol-acetone fermentation are reviewed. These techniques can be classified by product removal into gas phase (vacuum fermentation, ga s stripping), liquid phase (liquid-liquid extraction, aqueous two-phas e system), and solid phase (adsorption). Recent developments in separa tion techniques use membranes. Membrane separation techniques remove p roducts into gas phase (pervaporation) and into liquid phase (perstrac tion) using either solid or liquid membranes. Liquid extractants which are nontoxic to microorganisms are required at large quantities becau se of their poor distribution coefficients. The required amount of sol id adsorbents is also large. Gas stripping, pervaporation and perstrac tion share an advantage of clean product separation. Pervaporation and perstraction can overcome gas-liquid equilibrium unlike gas stripping , but have experienced flux limitation. This limitation can be resolve d by developing new membranes with higher flux. Since perstraction req uires alcohol recovery from extractants, pervaporation seems to be the most promising technique, but gas stripping is also attractive for la rge scale application.