Ethanol production from xylose with the yeast Pichia stipitis and simultaneous product recovery by gas stripping using a gas-lift loop fermenter withattached side-arm (GLSA)

The bioconversion of xylose into ethanol with the yeast Pichia stipitis CBS 5773 is inhibited when 20 g/L of ethanol are present in the fermentation b roth. In order to avoid this limitation, the fermentation was carried out w ith simultaneous recovery of product by CO, stripping. The fermentation was also improved by attaching a sidearm to the main body of a classical gas-l ift loop fermenter. This side-arm increases the liquid circulation, mass tr ansfer, and gas distribution, reducing the amount of oxygen in the inlet ga s necessary to perform the fermentation of xylose under microaerobic condit ions (K(L)a congruent to 16 h-l). The continuous stripping of ethanol from the fermentation broth in this new bioreactor system allowed the consumptio n of higher xylose concentrations than using Erlenmeyer shaker flasks, impr oved significantly the process productivity and provided a clean ethanol so lution by using an ice-cooled condenser system. Finally, a fed-batch fermen tation was carried out with a K(L)a = 15.8 h(-1). Starting with 248.2 g of xylose, 237.6 g of xylose was consumed to produce 88.1 g of ethanol which r epresents 72.6% of the theoretical yield (47.2 g/L of ethanol was recovered in the condenser, while 9.6 g/L remained in the fermentation broth). (C) 2 000 John Wiley & Sons, inc.