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bioweb.sungrant.org » Technical » Environmental » Life Cycle Analysis » Soybeans to Biodiesel

Life Cycle Assessment of Producing Biodiesel from Soybeans	Printer Friendly

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 (ISO 1997, 1998, 2000a, 2000b) and include guidelines to establish the goal and define the scope of the analysis (i.e., define methodologies, reference condition, system boundary, etc.), to conduct the inventory analysis (i.e., collect inputs/outputs and environmental burdens associated with the processes and normalize the environmental impacts to the reference conditions), to conduct the impact assessment, and to interpret the results.   Biodiesel production in the U.S. is currently limited but increasing. Most biodiesel used today is added to diesel fuel in a mixture of 20% biodiesel and 80% petroleum-derived diesel (B20).   In the process of making biodiesel, glycerin, soapstock, and soybean meal (used as animal feed) are also produced. To estimate the energy and environmental performance of the biodiesel only, the energy and environmental impacts are allocated to each product based on the equivalent product it is replacing. Thus the energy and environmental impacts of soybean meal are estimated based on their displacement of distiller’s dried grains and solubles (DDGS) in livestock feed rations (Kim, 2005b). Glycerin replaces glycerin made from petroleum and natural gas (Morrison, 2000; Overcash, 2000). Soapstock is not taken into account in the analysis due to its small quantity.   The soybean production practices and location of production are important considerations in the LCA. Environmental impacts associated with changes in soil characteristics (i.e., soil organic carbon; N2O, NOx, NO3- emissions from the soil) 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 (2004, 2005b) 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 (USDA NASS; USDA ERS). The analysis included the transportation of the soybeans on site and to the conversion facility.   Impacts on soil attributes (i.e., soil organic carbon dynamics, inorganic nitrate losses due to leaching, and nitrous oxide and nitrogen oxide emissions from soil) in each county were estimated using the DAYCENT model, the daily time step version of the CENTURY model which simulates long-term (100 to 1,000 year) soil carbon and nitrogen impacts for different ecosystems (e.g. agricultural crop production, prairie grass systems, etc.) resulting from changes in climate, land use, and management (Del Grosso 2000, 2001; Natural Resource Ecology Laboratory, 2005). The DAYCENT model simulates N2O, NOx and N2 emissions from soil resulting from nitrification and denitrification. DAYCENT requires information regarding temperature and precipitation, site-specific soil properties (i.e., soil texture, soil organic content, soil moisture content, and soil mineral content), and the current and historical cropping system.   The characterization factors for acidification, eutrophication and photochemical smog formation are adapted from the TRACI model (Tools for the Reduction and Assessment of Chemical and Other Environmental Impacts) (Bare, 2003). The conversion rate for biodiesel is one kg of biodiesel per 1.04 kg of soybean oil (Sheehan, 1998). Transportation of the biodiesel to retailers and use of the biodiesel assume that it is used as B20 in a city bus (Lyons, 2002). It is assumed that B20 fuel reduces the fuel economy of a diesel vehicle by 2% (http://www.fueleconomy.gov/). Results are estimated based on changes per kilometer traveled and are summarized in table 1.   The analysis estimated that driving one km on B20 reduced the amount of petroleum used (118.28 g), other fossil fuels used (8.71 MJ), and the amount of greenhouse gas emissions (588.04 g CO2 equivalent) compared to using diesel fuel. Eutrophication and photochemical smog formation are lower with biodiesel compared to petroleum-derived diesel fuel.   Sheehan (1998) concluded that biodiesel produced from soybeans reduced petroleum use and reduced carbon dioxide, carbon monoxide, particulate matter, and sulfur oxides emissions compared to petroleum derived diesel fuel. Nitrogen oxides and hydrocarbon emissions increased relative to petroleum diesel.

References
Bare, J. (2003). Tools for the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI): User's Guide and System Documentation. (EPA/600/R-02/052). United States Environmental Protection Agency. Del Grosso, S.J.; Parton, W.J.; & Mosier, A.R. [et al.] (2001). Simulated interaction of carbon dynamics and nitrogen trace gas fluxes using the DAYCENT model. In Modeling carbon and nitrogen dynamics for soil management (pp. 303–332). Boca Raton, FL: Lewis Publishers. Del Grosso, S.J.; Parton, W.J.; & Mosier, A.R. [et al.] (2000). General model for N2O and N2 gas emissions from soils due to denitrification. Global biogeochemical cycles, 14, 1045–1060. International Organization for Standardization (ISO) (1997). International organization for standardization 14040: Environmental management – Life cycle assessment – principles and framework. International Organization for Standardization. International Organization for Standardization (ISO) (1998). International organization for standardization 14041: Environmental management – Life cycle assessment – Goal and scope definition and inventory analysis. International Organization for Standardization. International Organization for Standardization (ISO) (2000a). International organization for standardization 14042: Environmental management – Life cycle assessment – Life cycle impact assessment. International Organization for Standardization. International Organization for Standardization (ISO) (2000b). International organization for Standardization 14043: Environmental management – Life cycle assessment – Life cycle interpretation. International Organization for Standardization. Kim, S.; & Overcash, M. (2000). Allocation procedure in multi–output process – an illustration of ISO 14041. International Journal of Life Cycle Assessment, 5, 221 – 228. Kim, S.; & Dale, B.E. (2002). Allocation procedure in ethanol production system from corn grain: I. system expansion. International Journal of Life Cycle Assessment, 7, 237–243 Kim, S.; & Dale, B.E. (2004). Cumulative energy and global warming impact associated with producing biomass for biobased industrial products, Journal of Industrial Ecology. 7, 147–162. Kim, S.; & Dale, B.E. (2005a). Environmental aspects of ethanol derived from no-tilled corn grain: nonrenewable energy consumption and greenhouse gas emission. Biomass & Bioenergy, 28, 475–489. Kim, S.; & Dale, B.E. (2005b). Life cycle assessment of various cropping systems utilized for producing biofuels: bioethanol and biodiesel. Biomass & Bioenergy, 29, 426 – 439. Kim, S.; & Dale, B.E. (2005c). Life cycle inventory information of the United States electricity system. International Journal of Life Cycle Assessment, 10, 294 – 304. Kim, S.; & Dale, B.E. (2006). Ethanol Fuels: E10 or E85 – Life Cycle Perspectives. International Journal of Life Cycle Assessment, 11, 117 – 121. Laser, M.; & Lynd, R.L., personal communications. May, 2005. Lyons, D.W. (2002). Biodiesel fuel comparison final data report. West Virginia University. Retrieved July 10, 2006,  from http://www.afdc.doe.gov/pdfs/wvu_biodiesel_report.pdf Morrison, L.R. (2000). Glycerol, Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley & Sons, Inc. Retrieved Jun 12, 2006,      from http://www.mrw.interscience.wiley.com/kirk/articles/glycmorr.a01/pdf_fs.html Natural Resource Ecology Laboratory (2005). Century soil organic matter model: user's guide and reference. Colorado State University. Retrieved July 9, 2006,       from http://www.nrel.colostate.edu/projects/century5/reference/index.htm Overcash, M. (2000). Gate–to–gate life cycle information of glycerine. North Carolina State University. Sheehan, J.; Camobreco, V.; & Duffield, J. [et al.] (1998). Life cycle inventory of biodiesel and petroleum diesel for use in an urban bus. (NREL/SR-580-24089). National Renewable Energy Laboratory. U.S. Department of Agriculture, Economic Research Service (http://www.ers.usda.gov/Data/CostsAndReturns/testpick.htm). U.S. Department of Agriculture, National Agricultural Statistics Service, (http://www.usda.gov/nass/pubs/estindx1.htm#agchem).