Environmental assessment of different technologies for bioethanol production from Cynara cardunculus: A Life Cycle Assessment study

Abstract

Waste biomass for biofuels production can contribute to reduce dependence on fossil fuels and consequently, a decrease of CO2 emissions. In this work, the environmental feasibility of cardoon-to-bioethanol process was evaluated using Life Cycle Assessment (LCA). For this purpose, three processes involving different biomass pretreatments (dilute acid (DA), single steam explosion (SE) and steam explosion + alkaline extraction (SE + AE)) were simulated by using SuperPro Designer 9.5. Simulation results and literature data were used to perform LCA by using Gabi 6.0 software. LCA results showed that the pretreatment step is the main contributor to the overall impact in the dilute acid case due to the large energy requirements. The use of steam-explosion-based pretreatments drastically reduce environmental impacts regarding to DA process, being fertilizers, chemicals and enzyme production the main important contributors. By combining single steam explosion and subsequent alkaline extraction, the environmental performance is improved compared to single steam explosion due to a reduction of the energy consumption. However, higher toxicity impacts were obtained mainly because of the larger amount of enzyme and chemicals required. GHG emissions and energy balance of bioethanol from cardoon falls within the values reported for similar lignocellulosic raw materials. Finally, the comparative study of bioethanol from cardoon and fossil gasoline indicates that steam explosion-based processes are environmentally superior in most impact categories, obtaining a dramatic reduction of the primary energy demand (80%) and the GHG emissions (45%).