Life cycle assessment of energy and GHG emissions during ethanol production from grass straws using various pretreatment processes
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The aim of this study was to perform a well-to-pump life cycle assessment (LCA) to investigate the overall net energy balance and environmental impact of bioethanol production using Tall Fescue grass straw as feedstock. The energy requirements and greenhouse gas (GHG) emissions were compared to those of gasoline to explore the potential of bioethanol as sustainable fuel.
The functional unit used in the study was 10,000 MJ of energy. The data for grass seed production were collected from the farmers in Oregon and published reports. The compositions of straw, pretreatment, and hydrolysis yields were obtained from laboratory experiments. Process models were developed for ethanol production using different pretreatment technologies in SuperPro Designer to calculate the process energy, raw materials, utility use, and emissions related. The Greenhouse Gases Regulated Emissions and Energy use in Transportation model and other literature studies were used to obtain additional data. Systematic boundary identification was performed using relative mass, energy, and economic value method using a 5% cutoff value.
Results and discussion
Ethanol yields from grass straw were estimated 256.62, 255.8, 255.3, and 230.2 L/dry metric ton of biomass using dilute acid, dilute alkali, hot water, and steam explosion pretreatments, respectively. Fossil energy required to produce one functional unit was in the range of −1507 to 3940 MJ for different ethanol production techniques. GHG emissions from ethanol LCA models were in the range of −131 to −555.4 kg CO2 eq. per 10,000 MJ of ethanol. Fossil energy use and GHG emissions during ethanol production were found to be lowest for steam explosion pretreatment among all pretreatment processes evaluated. Change in coproduct allocation from economic to mass basis during agricultural production resulted in 62.4% and 133.1% increase in fossil energy use and GHG emissions respectively.
Technologies used for ethanol production process had major impact on total fossil energy use and GHG emissions. N2O emissions from the nitrogen fertilizers were major contributor (77%) of total GHG emissions produced during agricultural activities. There was 57.43–112.67% reduction in fossil energy use to produce 10,000 MJ of ethanol compared to gasoline; however, about 0.35 ha of land is also required to produce this energy.
KeywordsE85 Grass straw Greenhouse gases Lignocellulosic ethanol Net energy Process model
This project was supported by Western Sun Grant Regional Centre, US Department of Transportation and Oregon Built Environment and Sustainable Technologies.
- Aden A, Ruth M, Ibsen K, Jechura J, Neeves K, Sheehan J, Wallace J, Montague L, Slayton A, Lukas J (2002) Lignocellulosic biomass to ethanol process design and economics utilizing co-current dilute acid prehydrolysis and enzymatic hydrolysis for corn stover. NREL/TP-510-32438. National Renewable Energy Laboratory, ColoradoGoogle Scholar
- Bossel U (2003) Well-to-wheel studies, heating values, and the energy conservation principle. European Fuel Cell Forum, OberrohrdorfGoogle Scholar
- Brander M, Tipper R, Hutchison C, Davis G (2009) Consequential and attributional approaches to LCA: a guide to policy makers with specific reference to greenhouse gas LCA of biofuels. Technical paper TP-090403-A, Ecometrica Press, London, UKGoogle Scholar
- Graf A, Koehler T (2002) Oregon cellulose–ethanol study. Oregon Office of Energy, SalemGoogle Scholar
- GREET (2010) The greenhouse gases, regulated emissions, and energy use in transportation model. Argonne National Laboratory, US Department of Energy. http://greet.es.anl.gov/main. Version 1.8d. Accessed January 10, 2011
- Kumar D, Murthy G (2011b) Pretreatments and enzymatic hydrolysis of grass straws for ethanol production in the Pacific Northwest US. Biol Eng 3(2):97–110Google Scholar
- Oregon Agricultural Enterprise Budgets (2010) http://arec.oregonstate.edu/oaeb/. Accessed April 10, 2011
- Taherzadeh MJ, Karimi K (2007) Enzymatic-based hydrolysis processes for ethanol from lignocellulosic materials: a review. Bio Resources 2(4):707–738Google Scholar
- Wang M (2005) Updated energy and greenhouse gas emission results of fuel ethanol. In: The 15th Int Symp Alcohol Fuels, San Diego, CA, SUAGoogle Scholar
- White JG (2000) Oregon perspectives on cellulose-to-ethanol. Oregon Office of Energy. http://www.nrbp.org/papers/029.pdf. Accessed October 20, 2011
- Wyman C (1996) Handbook on bioethanol: production and utilization. Taylor & Francis, WashingtonGoogle Scholar
- Xu J (2011) Alkaline pretreatment of switchgrass for ethanol production. Dissertation, North Carolina State University, RaleighGoogle Scholar