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Second generation bioethanol represents an interesting alternative for 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 (DA), Liquid hot water (LHW), Steam explosion (SE), Ammonia fiber explosion (AFEX) and Organosolv (OS) pretreatment are assessed using a combined economic value and environmental impact (EVEI) 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 co-generation 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, Dilute Acid can be considered the best pretreatment process to produce lignocellulosic bioethanol thanks to the best techno-economicenvironmental performences , with the largest economic and environmental margins with 39.2 M$/year and 83.9 kt CO2/year respectively.

Lignocellulosic ethanol is a promising alternative to replace liquid fossil fuels for the transportation sector in the near future. Organosolv pretreatment has been tested as a method for separating lignin from the biomass and commercializing it as a biopolymer. Based on published laboratory scale data we propose a feasible process flowsheet for organosolv pretreatment. Simulation of the pretreatment process provided mass and energy balances for a techno-economic analysis and the values were compared with the most prevalent and mature pretreatment method: diluted acid. Organosolv pretreatment required more energy, 578.1 MW versus 213.8 MW for diluted acid pretreatment, but resulted in a higher ethanol concentration after the biomass fermentation, 11.1% compared to 5.4%. Total annual costs (TAC) calculations showed advantages for diluted acid pretreatment but future improvements explored in the sensitivity analysis turned into possible savings of 42.8% in the minimum ethanol selling price (MESP) for organosolv pretreatment.

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Bioethanol from lignocellulosic feedstock rises as a promising alternative to replace liquid fossil fuels in the energy market for the next years. However, the variety of available biomass combined with the necessity of possible pretreatments and their particular features make it difficult to clearly identify the favorable process routes. In this study a systematic approach consisting of seven steps was proposed to obtain possible and feasible alternatives for the conversion of lignocellulosic biomass into bioethanol. The method was exemplified with the aid of a general case study, from the biomass selection to possible by-products generation. The case study resulted in a corn stover based process to produce bioethanol through ammonia fiber explosion pretreatment. Following the systematic approach different alternatives were proposed to finally obtain the optimal flowsheet with a minimum ethanol selling price of 0.43$/kg of ethanol, 35.4% lower than the initial process.

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