Extractive Batch Fermentation with CO2 Stripping for Ethanol Production in a Bubble Column Bioreactor: Experimental and Modeling

In alcoholic fermentation processes, ethanol is the main component that is toxic to yeast because it acts as a noncompetitive inhibitor of metabolism. One way of overcoming the inhibition effect on yeast is to extract the ethanol from the broth during the fermentation. The present work evaluates ethanol production by extractive batch fermentation using CO2 as a stripping gas. Investigation was first made of the influence of specific CO2 flow rate (ϕ) and solution temperature on ethanol stripping. The best results, in terms of ethanol removal, were obtained at 2.0 vvm and 34.0 °C. Modeling of conventional and extractive ethanol fermentation was then performed considering cell growth, substrate consumption, ethanol production, and the entrainment of ethanol and water using first-order equations. The hybrid Andrews–Levenspiel model was able to describe the kinetics of the conventional fermentation process, and a model proposed here could accurately predict the behavior of the extractive fermentation. In all the extractive fermentations, there was faster substrate uptake and earlier substrate exhaustion, compared to the conventional fermentation. Extractive fermentation, with stripping initiated after 3 h at an ethanol concentration of 43.3 g·L–1, resulted in an ethanol productivity (in g·L–1·h–1) that was around 25% higher, and finished about 2 h earlier, compared to the control fermentation.