Economic value and environmental impact analysis of lignocellulosic ethanol production: assessment of different pretreatment processes

Second-generation bioethanol represents an interesting alternative to liquid fuels in times of increased concerns over global warming and energy security. However, the recalcitrant structure of lignocellulosic biomass feedstock makes necessary a pretreatment process to increase the conversion of sugars. Diluted acid, liquid hot water, steam explosion, ammonia fiber explosion, and organosolv pretreatments are assessed using a combined economic value and environmental impact analysis under a full biorefinery setup in order to assess the best pretreatment process from a techno-economic-environmental point of view. Five process areas were identified within each process considered: pretreatment stage, conversion stage, product purification and separation stage, water treatment stage, and cogeneration stage. A process simulation software was used to consider material and energy balances of the biorefineries with different pretreatment processes and to optimize the separation and purification processes (e.g., distillation columns). For the considered biomass and scenarios, all processes resulted in positive gains in terms of economic feasibility and carbon dioxide emissions. In particular, diluted acid can be considered the best pretreatment process to produce lignocellulosic bioethanol thanks to the best techno-economic-environmental performances, with the largest economic and environmental margins of 39.2 M$/year and 83.9 kt CO2/year, respectively.