Biochemical and thermochemical conversion of wood to ethanol—simulation and analysis of different processes

Bioethanol as a transportation fuel offers various advantages. It can directly be used in existing transportation options and it can be produced by different conversion routes (i.e. thermochemical or biochemical processes) as well as from various types of feedstock (i.e. biomass containing sugar or starch, lignocellulosic biomass). Especially, the conversion of lignocellulosic biomass promises to improve the environmental performance, e.g. in terms of greenhouse gas emissions, and seems to have a better acceptance compared to sugar- or starch-based processes (i.e. food vs. fuel discussion). However, the process technology for the production of bioethanol from lignocellulosic biomass is still under development. Thus, within this paper, three basic process routes for ethanol from lignocelluloses are analysed from a systems point of view to allow for statements how the further technological development should be directed. For this reason, thermochemical gasification based on wood followed by alcohol synthesis and thermochemical gasification followed by syngas fermentation is compared to a process based on saccharification and subsequent fermentation. This analysis shows that ethanol yields exceeding the theoretical potential based on glucose cannot be reached with the analysed processes. Nevertheless, gasification with syngas fermentation and mixed alcohol synthesis is promising regarding alcohol yields as well as overall energy efficiencies, also compared to other options for liquid biofuels like Fischer–Tropsch diesel or methanol.