Vacuum fermentation integrated with separation process for ethanol production

In this study, continuous fermentation integrated with separation process at atmospheric and vacuum pressures are investigated. An initial glucose concentration of 200 g L−1 was used to produce yeast cells under batch operating mode. After a period of 18–20 h, a medium of 350 g L−1 glucose concentration was fed continuously to the fermentation-separation column. During the continuous experiments, fermented broth was recirculated back to the fermentation-separation column. At atmospheric pressure, the dry mass concentration decreased rapidly and remained at 2.4 g L−1 after long period, while glucose concentration still remained at 240 g L−1. On the other hand, at vacuum pressure, a quasi-steady state condition was reached after 96 h, corresponding to 4.2 g L−1 of cell dry mass, 165 g L−1 of glucose and 44.2 g L−1 of ethanol levels in the fermentation broth and 33.2 wt% of ethanol concentration at the outlet. These results indicate reduced product and substrate inhibition, suggesting that the integrated process could be used to replace the first bioreactor in a fermentation cascade system. A mathematical model was then developed and used to predict the kinetic parameters. The simulation results agreed well with experimental data.

► Fermentation reaction and separation of ethanol in the packed column.
► Kinetic parameters for the fermentation under the vacuum are predicted.
► A combination of CSTR mode and plug flow reaction mode for ethanol production.