CONTINUOUS ETHANOL-PRODUCTION BY ZYMOMONAS-MOBILIS IN A FLUIDIZED-BED REACTOR .1. KINETIC-STUDIES OF IMMOBILIZATION IN MACROPOROUS GLASS-BEADS

A model has been developed to calculate the ethanol production in a well-mixed fluidized bed reactor. This model takes into account diffusion and the reaction inside porous glass beads and the activity of suspended cells in the fluidized bed reactor. The associated model parameters have been determined from the literature and by kinetic studies with Zymomonas mobilis in a continuous stirred tank reactor. The model permits good predictions of steady-state data in a fluidized bed reactor at residence times longer than 1-1.5 h. The immobilization of Z. mobilis in a fluidized bed reactor results in high ethanol space-time yields of more than 50 g . l-1 . h-1 at a glucose conversion of 80% (glucose in substrate: 120 g l-1). At 99% conversion a space-time yield of 30 g . l-1 . h-1 can be achieved when two fluidized bed reactors operate as cascade.