(542c) Life Cycle Analysis of Alternatives for Diesel: An Assessment of Inputs, Study Assumptions and Feedstock Type

With an increasing focus on renewable fuels and rising petroleum costs, it is vital to understand the environmental impacts from various alternative fuel products and processes. Biofuels are now seen as one of the simplest and most practical short-term fuel solutions. Substitutes for petroleum diesel are already widely popular in Europe, and gaining support in the US. Furthermore, current and future legislation aimed at assuring sustainability could result in regulation of biofuels by including greenhouse gas emission reduction and biodiversity requirements as determined by life cycle assessment (LCA). This further raises the need for a thorough grasp of the impacts of biofuels. Biodiesel and green diesel are the two most common diesel substitutes. Biodiesel is created through a transesterification reaction, producing a methyl ester which has similar properties to petroleum diesel. Green diesel is created through a catalyzed hydrogenation reaction on the plant oil, creating a liquid hydrocarbon fuel exhibiting superior performance for some properties compared to petroleum diesel. Syndiesel, another diesel fuel substitute, is created through high temperature and pressure gasification/catalytic reactions, from biomass, natural gas, or coal. To select from such a broad range of alternative diesel fuels will be challenging, but can be aided by a comprehensive environmental assessment.

Differences in study assumptions account for large variability in LCA impacts, making research into the effects of study assumptions important. The most important LCA study assumptions include methods of allocating inventory data among co-products, with or without farm emissions of N2O, land use change emissions, and feedstock type. To address these issues, this study characterized the greenhouse gas emissions, total energy, and fossil energy demand for biodiesel, green diesel, and syndiesel, and further analyzed the impacts of changing feedstock. The feedstock impacts are an ongoing activity in our laboratory, but plant oil feedstocks including algae, canola, jatropha, palm, rapeseed, soybeans, and sunflower will be reported on in this presentation. For syndiesel, feedstocks considered were wood residues, natural gas, and coal. Allocation methods based on product mass, energy content, and displacement were investigated in separate case studies.

Methods

Inventory data were obtained from several literature sources; from the US Department of Energy, from the European Joint Research Council of CONCAWE, from peer-reviewed publications, as well as biofuel processing data supplied by UOP LLC. As for the various life cycle stages, cultivation and feedstock processing data was obtained from literature sources covering a range of plant cultivation and geographic settings. SimaPro 7, a LCA software tool, providing data for some chemicals, electricity, heat, and other processes. Data for conversion from feedstock to fuel was provided by UOP LLC for biodiesel and green diesel, and for syndiesel, data came from government reports and publications. Data for N2O emissions from farm land due to fertilization was obtained from the various literature sources and also estimated using correlations from the most recent IPCC reports. Land use change is a complicated issue with very little agreement between studies. The clearing of land creates a ?carbon debt?, and literature sources give ranges from 5 years to 400 years for the time to pay this debt down when biofuels are produced and used. Our research will better understand this complex issue, and reduce the uncertainty of land use change.

Results

Preliminary results obtained to date in our laboratory show that biodiesel has exhibits a savings of between 48% and 65% in life cycle fossil energy demand over petroleum diesel, and savings of between 37% and 73% in greenhouse gas emissions. The ranges cited are a result of study assumptions with regard to inventory inputs, allocation method and feedstock type. Green diesel has life cycle fossil energy demand savings between 67% and 86% over petroleum diesel, and greenhouse gas savings between 42% and 85%. Syndiesel shows cumulative fossil energy demand ranging from 98% savings to a 51% increase over petroleum diesel, and greenhouse gas emissions range from a 91% reduction in emissions to a 115% increase, depending on fuel feedstock. Our preliminary results show green diesel having lower fossil energy and GHG impacts over the life cycle than biodiesel. Syndiesel results are very dependent on feedstock type, but can be either beneficial or detrimental. The effects of N2O could account for as much as 60% of the greenhouse gas footprint of a biofuel. Further investigation is underway to better understand the emissions of N2O from the field, a major contributor to the overall nitrous oxide emissions. Our continued research will help understand the reasons for these variations, and what effects are caused by the study assumptions chosen. Furthermore, the importance of input data is critical, and ensuring that the data comes from a reliable source. This study will bring all of these factors together for a comprehensive review on life cycle assessment, in the context of diesel fuel alternatives.