Effects of Operational and Geometric Variables of a Bubble Column Bioreactor on Ethanol Stripping with CO2: Liquid and Gas-Phase Monitoring

The effects of headspace height and specific gas flow rate on the performance of ethanol removal by CO2 stripping in a bubble column bioreactor were investigated. Stripping experiments were carried out using an ethanol solution with the liquid and gas phase compositions being monitored over time. The results showed that the ethanol removal constant (k E) increased with the increase of the reactor headspace. A dimensionless correlation for the Sherwood number was obtained, enabling the prediction of k E by considering different design variables and operating conditions. A good agreement was obtained between the experimental data and the values predicted by the model, indicating that the correlation was able to describe the behavior of the process with high accuracy. Simulations of extractive ethanol fermentations showed an increase of 13.5% in volumetric ethanol productivity when the headspace height with respect to the total height increased almost three times, in an extractive fed-batch fermentation performed with a high substrate concentration in the must feed. The specific energy values for ethanol production in the new system were 76.3 and 78.4% lower for the simulated extractive ethanol fermentations conducted in batch and fed-batch modes, respectively. Therefore, the greater the headspace height, the greater the ethanol volumetric productivity, and the lower the energy requirement for ethanol production.