(542f) Life Cycle Assessment of Renewable Transportation Fuel Feedstocks

Authors: 
Murphy, C. F., University of Texas at Austin
Hebner, R., University of Texas at Austin
Webber, M., University of Texas at Austin


Understanding the potential impact of large-scale production and use of alternative biofuel systems requires characterization and assessment of material and energy flows over the entire life cycle. ?Well-to-wheel? analyses are being conducted for four potential, emerging renewable feedstocks suitable for production of transportation fuels: 1) ethanol from sugar cane; 2) ethanol from citrus waste; 3) biodiesel from cottonseed; and 4) biodiesel from algae. These biofuels are compared to four existing fuel systems: gasoline, corn ethanol blends (E85), soybean biodiesel, and petroleum diesel. The framework used to evaluate these feedstocks and fuels is a set of process-flow models that account for inputs and outputs and which are designed for economic and environmental assessment and comparison. The process flow models, developed for all eight feedstocks, are designed to be dyanamic and modular; the inputs are thus parametric and the modules are developed at the unit operation level. In combination, the modules cover the full life cycle of the various fuels systems from raw material acquisition through vehicle combustion, with appropriate allocation of by-products. Detailed, quantitative, activity-based models are designed to address agricultural activities, transportation to processing facilities, conversion of feedstocks into fuels for powering passenger vehicles, and fuel delivery systems. Environmental metrics considered in the study include net energy, water use, land use, and emissions to air (both greenhouse gases and criteria pollutants). The geographic boundaries are the U.S., with the exception of petroleum feedstock production, in which case both domestic and foreign supplies are included. Assessment of the environmental impact of fuel combustion (i.e., the use phase) will be performed separately by modeling emission profiles and by incorporating the results into photochemical air quality modeling simulations to estimate regional air quality impacts. The final outcome of this project is expected to be an environmental characterization of emerging renewable feedstocks and fuels, along with an evaluation of potential economic and technological barriers to widespread adoption. Results will be presented in such a manner as to be understood by the general public, thus facilitating more informed choices by both consumers and policymakers. Furthermore, the flexible, dynamic nature of the models will facilitate evaluation of additional fuels systems of interest.