a b s t r a c t
Ethanol production from lignocellulosic materials is often conceived considering independent, standalone production plants; in the Brazilian scenario, where part of the potential feedstock (sugarcane bagasse) for second generation ethanol production is already available at conventional ﬁrst generation production plants, an integrated ﬁrst and second generation production process seems to be the most obvious option. In this study stand-alone second generation ethanol production from surplus sugarcane bagasse and trash is compared with conventional ﬁrst generation ethanol production from sugarcane and with integrated ﬁrst and second generation; simulations were developed to represent the different technological scenarios, which provided data for economic and environmental analysis. Results show that the integrated ﬁrst and second generation ethanol production process from sugarcane leads to better economic results when compared with the stand-alone plant, especially when advanced hydrolysis technologies and pentoses fermentation are included.
1. Introduction Increasing concerns about climate change and energy security have motivated the search for alternative forms of energy (Karuppiah et al., 2008). Since the transportation sector is responsible for a signiﬁcant fraction of the greenhouse gases emissions, substitution of oil derived fuels by biofuels, like ethanol, could signiﬁcantly decrease environmental impacts, besides providing gains on the socio-economic levels as well. Brazil and the US are the world’s largest bioethanol producers, using sugarcane and corn as feedstock, respectively. In the Brazilian sugarcane industry, large amounts of lignocellulosic materials (sugarcane bagasse and trash) are produced during sugar and ethanol production. Sugarcane bagasse is currently used as fuel, supplying the energy required for the plant, while sugarcane trash, previously burnt to improve the harvest procedure, is today mostly left in the ﬁeld for agricultural purposes (Alonso Pippo et al., 2011). Therefore, banning of burning practices signiﬁcantly improved the amount of sugarcane trash available for use in the industry (Seabra et al., 2010).
Second generation bioethanol, produced from lignocellulosic materials, has been envisioned as the biofuel with the largest potential to replace fossil derived fuels with lower impacts than the conventional, ﬁrst generation bioethanol (Martín and Grossmann, in press; Ojeda et al., 2011; Seabra et al., 2010). Besides being cheap and abundant, production of lignocellulosic materials has limited competition with food production, thus they do not comˇ ˇ promise food security (Alvira et al., 2010; Cucek et al., 2011). In the sugarcane industry another advantage for the use of lignocellulosic material as feedstock for bioethanol production is clear: since they are already available at plant site (for bagasse), or close to it (trash), second generation bioethanol production may share part of the infrastructure where ﬁrst generation ethanol production takes place (for instance concentration, fermentation, distillation, storage and cogeneration facilities). In addition, potential fermentation inhibitors generated in the lignocellulosic material pretreatment may have a decreased effect on fermentation yields, since the hydrolyzed liquor may be fermented mixed with sugarcane juice, diluting these inhibitors. Nevertheless, the recalcitrance of lignocellulosic materials hinders the transformation of cellulose into fermentable sugars; the second generation ethanol production processes therefore require more sophisticated equipment and investment than conventional ﬁrst generation ethanol production (Nigam and Singh, 2011). Since second generation ethanol production is not yet a commercial reality, different process conﬁgurations have been investi-
M.O.S. Dias et al. / Bioresource Technology 103 (2012) 152–161
gated in order to develop efﬁcient conversion...