SIMULTANEOUS FERMENTATION AND SEPARATION IN THE ETHANOL AND ABE FERMENTATION

Simultaneous separation of solvent products during fermentation reduces product inhibition and increases reactor productivity. Separation techniques 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, gas stripping), liquid phase (liquid-liquid extraction, aqueous two-phase system), and solid phase (adsorption). Recent developments in separation techniques use membranes. Membrane separation techniques remove products into gas phase (pervaporation) and into liquid phase (perstraction) using either solid or liquid membranes. Liquid extractants which are nontoxic to microorganisms are required at large quantities because of their poor distribution coefficients. The required amount of solid adsorbents is also large. Gas stripping, pervaporation and perstraction 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 resolved by developing new membranes with higher flux. Since perstraction requires alcohol recovery from extractants, pervaporation seems to be the most promising technique, but gas stripping is also attractive for large scale application.