Thermodynamic analysis and potential efficiency improvements of a biochemical process for lignocellulosic biofuel production

This paper presents a thermodynamic analysis of a biochemical process for the production of bioethanol from a lignocellulosic feedstock. The major inefficiencies in the process are identified as: i) the combustion of lignin for process heat and power production and ii) the simultaneous saccharification and fermentation process. As lignin is not converted to ethanol and lignin has a high value of chemical exergy, the overall efficiency of the biochemical process largely depends on how the lignin is utilized. We therefore consider integrating a source of low temperature heat, such as waste heat or low-enthalpy geothermal heat, into a biochemical lignocellulosic biorefinery to provide process heat. This enables the lignin-enriched residue to be used either as a feedstock for chemicals and materials or for on-site electricity generation. Our analysis shows that integrating low temperature heat source into a biorefinery in this way represents an improvement in overall resource utilization efficiency.