9-19: Simulation and optimization of an extractive fermentation process for bioethanol production

Extractive fermentation processes for bioethanol production are advantageous when compared to traditional modes of operation for presenting higher productivity, less water consumption, low vinasse generation and low utilities use for cooling the fermentors.

The process studied in this work consists of a stirred bioreactor linked to a hollow-fiber membrane and a flash vessel under vacuum (for ethanol removal). The high productivity is achieved due to effects of high S. cerevisiae and low ethanol concentrations in the system.

The objective of this work is to simulate and optimize the operational conditions of the flash vessel, such as flow rate, temperature and pressure, focusing on the maintenance of the ethanol concentration at 40 Km/m³ in the bioreactor and on the minimization of water loss in the flash separation. It is well known that at the concentration of 40 Kg/m³, ethanol does not inhibit S. cerevisiae growth and presents an inhibitory effect on fermentation contaminants. On the other hand, the reduction of water content in the top stream of the flash vessel results in a lower fresh water feeding requirement to dilute process medium.

The ASPEN PLUS software will be used to simulate the effect of operational conditions of the flash vessel in the streams and bioreactor compositions.

NRTL (Nonrandom two-liquid) model will be considered in the thermodynamic package of ASPEN PLUS. The complexity of this work is due to the great number of components in the fermentation broth, which change significantly the ethanol-water thermodynamic equilibrium even in low concentrations.