Life Cycle Assessment (LCA) of biodiesel from soybeans is a cradle to grave evaluation of energy and environmental issues associated with producing, harvesting, and transporting soybeans, converting the soybeans into biodiesel, and distributing and using the biodiesel in motor vehicles. Soybean biodiesel LCAs frequently include an assessment of diesel fuel, the petroleum derived product that biodiesel will displace, as a means to compare the two products. Energy and environmental issues examined include crude oil used, nonrenewable energy consumption, greenhouse gas emissions, photochemical smog formation, acidification, and eutrophication. LCA methodologies have been standardized by the International Organization for Standardization.
Biodiesel production in the U.S. is currently limited but is increasing. Most biodiesel used today is added to diesel fuel using a mixture of 20% biodiesel and 80% petroleum-derived diesel (B20).
In the process of making biodiesel from soybeans, glycerin and soybean meal are also produced. To estimate the energy and environmental performance of the biodiesel only, the energy and environmental impacts of displacing distiller’s dried grains with soybean meal in livestock feed rations, and displacing fossil fuel derived glycerin with glycerin from biodiesel production are accounted for. The location and management practices used for soybean production are important considerations as the environmental impacts associated with changes in soil characteristics (i.e., erosion, carbon; nitrogen cycling) vary with soil type and physical characteristics (e.g., slope), climate, and tillage and other management practices. Soybean yields and fertilizer and chemical input levels are also important considerations.
Kim and Dale evaluated the production of biodiesel from soybeans for Hardin County, IA and its adjacent counties. Soybean production assumed no-till planting and average yields, fertilizer and chemical inputs, and fuel use for the years 2001 to 2003. The analysis included the transportation of the soybeans on site and to the conversion facility. Impacts on soil attributes were estimated using the DAYCENT model which simulates changes in soil characteristics resulting from changes in climate, land use, and management practices. Transportation of the biodiesel to retailers and use of the biodiesel assume that it is used as B20 in a city bus.
The analysis estimated that driving one mile on B20 reduced the amount of petroleum used, other fossil fuels used, and the amount of greenhouse gas emissions compared to using diesel fuel. Compounds that can potentially produce dead zones in aquatic systems (i.e., nitrogen and phosphorus fertilizers) and that are involved in smog formation are reduced with biodiesel use relative to the use of petroleum-derived diesel fuel.
Sheehan (1998) concluded that biodiesel produced from soybeans reduced petroleum use, emissions of carbon compounds, emissions of sulfur compounds, and particulate matter emissions compared to petroleum-derived diesel fuel. Emissions of nitrogen compounds and hydrocarbon emissions increased relative to petroleum diesel.