Ethanol production by immobilised yeast and its CO2 gas effects in a packed bed reactor

Abstract

AbstractImmobilised yeast trapped in an alginate matrix demonstrated maximum activity at 30°C and showed no pH effect between 3 and 7. Substrate inhibition was observed at glucose concentrations above 8% but the immobilised cells retained 70% of their maximum activity at 20% glucose concentration. The operational stability of immobilised cells was lower in simple glucose solution than in the activation medium in which only 20% of the activity was lost after 10 days operation. Inactivated immobilised yeast beads were reactivated by incubation in activation medium without a significant increase in cell numbers in a bead. During the operation of the immobilised yeast in a packed bed reactor, CO2 gas accumulation adversely affected the reactor performance. An ideal plug flow reactor, not taking into account the formation of CO2 gas bubbles and the presence of mass transfer resistance, was simulated using a kinetic model for the production of ethanol and the simulation results were compared with the actual reactor performance to determine the CO2 gas effect, quantitatively. Up to 45 % of the substrate conversion was lost due to the accumulation of CO2 gas bubbles in all cases.