Location: Sustainable Biofuels and Co-Products
Title: A reassessment of life cycle greenhouse gas emissions for soybean biodiesel Authors
|Pradhan, Anujp -|
|Shrestha, Dev -|
|Gerpen, Van -|
|Duffield, James -|
Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 16, 2012
Publication Date: N/A
Interpretive Summary: Chemical species such as carbon dioxide and nitrogen oxides, when released into the atmosphere, contribute to global climate change. Because they cause the earth to retain some of the heat generated when solar radiation hits the earth, they are referred to as 'greenhouse gases' (GHG). In evaluating a new technology to determine its environmental impact, a key component is the calculation of its contribution to global GHG levels. Such a calculation was conducted nearly two decades ago for biodiesel produced from soybeans, and indicated that biodiesel produced 78% less GHG than did petroleum diesel fuel. Because there have been substantial changes in agricultural practices since that calculation was conducted, it is appropriate to reassess the GHG contributions of petroleum and biodiesel. Such calculations are the subject matter of this paper. The results indicate that with todays technologies, especially due to improvements in agriculture and in the methods of extracting soybean oil from soybeans, the GHG contribution of soybean biodiesel is now 84% less than that of petroleum-based diesel fuel. That is, improvements in technology over the past two decades have resulted in a nearly 8% further reduction in GHG production compared to that associated with the production and combustion of petroleum diesel fuel.
Technical Abstract: Since the first comprehensive soybean biodiesel (BD) LCA by the National Renewable Energy Laboratory in 1998, there have been many technological improvements that could change the LCA results. This study updates the GHG emissions for BD using the most current set of agriculture data from the year 2006. The updated results showed that the GHG emissions for BD are reduced by 81.3% compared to 2005 baseline diesel. Agricultural lime accounted for 50.5% of GHG from all agricultural inputs. Soil nitrous oxide accounted for 17.9% of total agricultural emissions. This study found that soybean meal and oil prices had significant positive correlation and hence argued that system boundary expansion without co-product allocation for indirect land use change produces erroneous result. When the emissions associated with predicted indirect land use change were allocated and incorporated using US EPA model data, the GHG reduction from BD was 76.5% lower than baseline diesel.