Life Cycle Analysis of Soybean Biodiesel Production

Developing renewable fuels, such as biodiesel, is desirable because they are derived from sustainable sources of energy, whereas petroleum fuels come from a finite resource that is rapidly being depleted. However, the production of renewable fuels generally involves a significant amout of fossil energy. The renewability of biofuel is largely a factor of the amount of fossil energy used for its production, hence it is essential to estimate the amount of fossil energy used over the entire life cycle of the biodiesel production. The comprehensive Life Cycle Analysis (LCA) of soybean biodiesel production was conducted by National Renewable Energy Laboratory (NREL) in 1998. Because of increasing changes in land use and production process, the LCA conducted few years ago is no longer representative of current practices. This research updated the Energy Life Cycle Analysis (ELCA) of the NREL model and estimated the Fossil Energy Ratio (FER) to be 4.56 based on data from 2002 soybean production in the United States. This is a significant improvement (43%) over the 1998 NREL study that reported a FER of 3.2. The United States Department of Agriculture (USDA) projects soybean yield to increase annually by 0.4 to 0.5 bushel/acre through the year 2017. For every one bushel increase in soybean yield, FER increases by about 0.45 percent. Holding all other variables constant, the FER of soybean biodiesel is estimated to reach 4.69 in the year 2015 when soybean yield is projected to increase to 45.3 bushels per acre. The FER will continue to improve overtime with increasing trend of soybean yield and improvement in the energy efficiency of the crushing and biodiesel plants. In addition to ELCA, four commonly referenced models were compared for the GHG emission savings. The analysis revealed that the most significant factors in altering the results in GHG emissions were differences in data citations, system boundaries, and coproduct allocations.