Techno-Economic Evaluation of Bioethanol Production from Three Different Lignocellulosic Materials

The lignocellulosic materials spruce (softwood), Salix (hardwood) and corn stover (agricultural residue) are all potential feedstock for ethanol production. In this study the utilization of these materials for bioethanol production was compared in terms of production cost and energy demand using a process concept based on SO2-catalysed steam pretreatment followed by simultaneous saccharification and fermentation (SSF). A model including all major process steps was implemented in the commercial flowsheeting program Aspen Plus, and the model input was based on data recently obtained on lab scale or in a process development unit.
The main focus of the study was on the pretreatment and the SSF steps. Sensitivity analyses of important process parameters showed their relative effects on the production cost and on the potential for cost reduction for each raw material. The study clearly demonstrates the importance of a high ethanol yield and the necessity of utilizing the pentose fraction for ethanol production to obtain good process economy, especially when using Salix or corn stover. Furthermore, a less energy-demanding process, here mainly achieved by increasing the dry matter content in SSF, reduces the capital cost and results in higher co-product credit, and therefore has a significant effect on the overall process economy.