469948 Climate Change Impacts of Bioethanol Production from Willow
The use of cellulosic biofuels is projected to increase in order to offset greenhouse gas (GHG) emissions from the combustion of non-renewable fuels. Hot water extraction (HWE) is a potential pretreatment step for multi-pathways biorefinery to yield natural, wood-based chemicals and materials. A cradle-to-grave life cycle assessment (LCA) was performed to assess the GHG emissions associated with the production of 1 MJ of ethanol by fermentation of sugar derived from HWE of willow biomass. The system boundary includes cultivation and harvesting of willow, transportation from the field to the biorefinery, hot-water extraction, fermentation and separation of ethanol, as well as the transportation of ethanol and its combustion. The system boundary was expanded to include co-products and underground carbon sequestered. Two conversion scenarios were considered. In the first scenario, electricity and heat required for the processes are cogenerated on site by the combustion of a fraction of the extracted willow biomass. In the second, electricity for the processes is supplied exclusively by the national grid. A sensitivity analysis and Monte Carlo analyses were performed for each scenario. Preliminary results show that GHG emissions for scenario one are -36.9 g CO2eq MJ-1. For scenario two, GHG emissions increase to 117.9 g CO2eq MJ-1. The amount of yeast used and the yield of willow were the most sensitive variable parameters. The fermentation and distillation of ethanol accounts for up to 70% of the total greenhouse gas emissions. The source of heat and electricity is the main driver in reducing greenhouse gas emissions when gasoline is replaced by ethanol produced from sugars that are extracted by HWE of willow.
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