Comparative Life Cycle Assessment of Lignocellulosic Ethanol Production: Biochemical Versus Thermochemical Conversion |
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Authors: | Dongyan Mu Thomas Seager P Suresh Rao Fu Zhao |
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Institution: | 1. School of Civil Engineering and Ecological Science and Engineering Interdisciplinary Graduate Program, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN, 47907, USA 2. Golisano Institute for Sustainability, Rochester Institute of Technology, 111 Lomb Memorial Drive, Rochester, NY, 14623, USA 3. School of Civil Engineering, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN, 47907, USA 4. School of Mechanical Engineering and Division of Environmental and Ecological Engineering, Purdue University, 585 Purdue Mall, West Lafayette, IN, 47907, USA
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Abstract: | Lignocellulosic biomass can be converted into ethanol through either biochemical or thermochemical conversion processes. Biochemical
conversion involves hydrolysis and fermentation while thermochemical conversion involves gasification and catalytic synthesis.
Even though these routes produce comparable amounts of ethanol and have similar energy efficiency at the plant level, little
is known about their relative environmental performance from a life cycle perspective. Especially, the indirect impacts, i.e.
emissions and resource consumption associated with the production of various process inputs, are largely neglected in previous
studies. This article compiles material and energy flow data from process simulation models to develop life cycle inventory
and compares the fossil fuel consumption, greenhouse gas emissions, and water consumption of both biomass-to-ethanol production
processes. The results are presented in terms of contributions from feedstock, direct, indirect, and co-product credits for
four representative biomass feedstocks i.e., wood chips, corn stover, waste paper, and wheat straw. To explore the potentials
of the two conversion pathways, different technological scenarios are modeled, including current, 2012 and 2020 technology
targets, as well as different production/co-production configurations. The modeling results suggest that biochemical conversion
has slightly better performance on greenhouse gas emission and fossil fuel consumption, but that thermochemical conversion
has significantly less direct, indirect, and life cycle water consumption. Also, if the thermochemical plant operates as a
biorefinery with mixed alcohol co-products separated for chemicals, it has the potential to achieve better performance than
biochemical pathway across all environmental impact categories considered due to higher co-product credits associated with
chemicals being displaced. The results from this work serve as a starting point for developing full life cycle assessment
model that facilitates effective decision-making regarding lignocellulosic ethanol production. |
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