Abstract
In Europe, ethanol is blended with gasoline fuel in 5 or 10% volume (E5 or E10). In USA the blend is 15% in volume (E15) and there are also pumps that provide E85. In Brazil, the conventional gasoline is E27 and there are pumps that offer E100, due to the growing market of flex fuel vehicles. Bioethanol production is usually by means of biological conversion of several biomass feedstocks (first generation sugar cane in Brazil, corn in the USA, sugar beet in Europe, or second-generation bagasse of sugarcane or lignocellulosic materials from crop wastes). The environmental sustainability of the bioethanol is usually measured by the global warming potential metric (GWP in CO2eq), 100 years time horizon. Reviewed values could range from 0.31 to 5.55 gCO2eq/LETOH. A biomass-to-ethanol industrial scenario was used to evaluate the impact of methodological choices on CO2eq: conventional versus dynamic Life Cycle Assessment; different impact assessment methods (TRACI, IPCC, ILCD, IMPACT, EDIP, and CML); electricity mix of the geographical region/country for different factory locations; differences in CO2eq factor for CH4 and N2O due to updates in Intergovernmental Panel on Climate Change (IPCC) reports (5 reports so far), different factory operational lifetimes and future improved productivities. Results showed that the electricity mix (factory location) and land use are the factors that have the greatest effect (up to 800% deviation). The use of the CO2 equivalency factors stated in different IPCC reports has the least influence (less than 3%). The consideration of the biogenic emissions (uptake at agricultural stage and release at the fermentation stage) and different allocation methods is also influential, and each can make values vary by 250%.
Highlights
Energy-related carbon dioxide (CO2 ) emissions, mostly due to fuel burning, were of 29 gigatonnes (Gt) in 2007, 34 Gt in 2011, and are expected to increase to 40 Gt until 2030 [1], contributing to the potential increase of global average temperatures of about 6 ◦ C, even including the global production of 120 million tonnes of oil equivalent (Mtoe) of biofuels [2,3]
We aim to evaluate the differences in GWP metric (CO2 eq) results if we consider dynamic Life Cycle Assessment (LCA) instead of conventional LCA; the influence of the factory geographical placement by means of different electricity mixes; the difference in considering updated Intergovernmental Panel on Climate Change (IPCC) (100-year time horizon) CO2 equivalency factor for CH4 and N2 O; the difference in considering a 20- instead of 100-year time horizon; and the influence of considering different impact category methods for the same GWP metric, e.g., TRACI 2005 2.1, IPCC GWP 20 years 1.01, ILCD 2011 Midpoint+ 1.07, IMPACT
From our study we found that the same deviations were as follows, considering the different topics analyzed: Impact assessment methods up to 30%, location of the factory up to
Summary
Energy-related carbon dioxide (CO2 ) emissions, mostly due to fuel burning, were of 29 gigatonnes (Gt) in 2007, 34 Gt in 2011, and are expected to increase to 40 Gt until 2030 [1], contributing to the potential increase of global average temperatures of about 6 ◦ C, even including the global production of 120 million tonnes of oil equivalent (Mtoe) of biofuels [2,3]. Ethanol has a high octane number and a reduced tendency to create knocking in spark ignition engines. It allows for low-temperature combustion, due to its oxygen content, contributing to the reduction of carbon monoxide (CO) and nitrous oxides (NOx) emissions [5].
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