Second-Generation Ethanol: The Need is Becoming a Reality

摘要

Bioethanol is currently one of the most important sources of renewable fuel and has the potential to partially replace petroleum-based liquid fuels. The United States is the largest ethanol producer in the world, with an average production of 54 billion liters per year. Most of its production derives from cornstarch. The Carbon Intensity Index (CI) for cornstarch-derived ethanol-75.97 g of carbon dioxide equivalent (CO_(2e)) emitted per megajoule (MJ) of energy produced-is close to the gasoline index (95.86 g of CO2e/MJ), and the use of cornstarch-derived ethanol has little impact on the emission of greenhouse gases. Compared to ethanol from cornstarch, production using sugarcane has a lower CI (56.66 g of CO2e/MJ), and greater emission reductions can be achieved by replacing gasoline or other fuels with ethanol obtained from sugarcane. Brazil, the second largest world producer of ethanol, produces about 25 billion L/y of ethanol and has the largest flex-fuel vehicle fleet in the world. Nevertheless, the Brazilian ethanol sector is in a state of economic stress caused mainly by the high operational costs and the fact that sugarcane productivity seems to have reached a plateau. In this scenario, conversion of the sugars present in lignocellulosic biomass into ethanol emerges as a promising technology with the potential to revolutionize the renewable fuels sector. In this review, we present the advances and challenges in producing and fermenting lignocellulosic sugars, demonstrating the huge potential that this technology represents for the renewable fuels sector.