Vacuum-Assisted Gas Stripping Extractive Fermentation for Process Intensification of Sorghum-Based Bioethanol Production: An Experimental and Modeling Study.

Extractive fermentation can mitigate the inhibitory effects of ethanol on yeast cells by continuously removing ethanol as it is produced, thereby enhancing ethanol productivity during the sorghum hydrolysate fermentation. This approach represents a promising strategy for process intensification in starch-based bioethanol production, particularly in systems limited by product inhibition. The present study describes the modeling and experimental validation of ethanol production in separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) processes, utilizing vacuum-assisted gas stripping for in situ ethanol removal. Initially, kinetic parameters for saccharification and fermentation were determined separately. Subsequently, SSF experiments were conducted to evaluate the predictive capability of the proposed model. Finally, extractive SHF and SSF experiments were carried out in a 2-liter bubble column bioreactor under vacuum-assisted gas stripping conditions. The proposed model for SHF and SSF processes, based on mass balances for liquefied starch (St), glucose (G), and ethanol (E), and incorporating saccharification and fermentation kinetics with product inhibition, showed strong agreement with the experimental data for both conventional and extractive fermentations, achieving R2 values above 0.99. Furthermore, vacuum-assisted gas stripping proved to be an effective process intensification strategy, increasing ethanol productivity by up to 60%. These results highlight its potential for improving ethanol production from starch-based substrates.