Bioreactor and process design for 2G ethanol production from xylose using industrial S. cerevisiae and commercial xylose isomerase

Second-generation ethanol has gained attention since the increase in demand for renewable fuels, but some issues still impair its feasibility, such as the conversion of xylose from biomass. Many routes can be explored for this purpose, but Simultaneous Isomerization and Fermentation (SIF) stand out due to the possibility of working with robust, non-genetically modified Saccharomyces cerevisiae strains. This work addresses bioreactor and process designs for SIF, using high enzyme and yeast load in their commercial forms, that can be introduced in the current ethanol-sugar industry. Characterization of two xylose isomerases (IGI-HF and Sweetzyme) in SIF conditions showed that both are suitable for the process. Between two industrial yeast strains evaluated, S. cerevisiae “Itaiquara” (baker’s yeast) was selected due to its superior xylulose assimilation. Problems with mass transfer and cell damage due to the presence of enzyme particles at high loads were faced, and different strategies were evaluated. Promising ethanol productivity (0.87 gEtOH/L/h, for 50 gDCW/L and 53,000 IU/L) was achieved using an enzyme-multiple-packed bed reactor. In addition, it allowed easy enzyme recovery and reuse, enabling its application in repeated batch operations integrated into the 1G ethanol process.