US EPA

5043674 

Journal Article 

Life cycle analysis of biochemical cellulosic ethanol under multiple scenarios 

Murphy, CW; Kendall, A 

2015 

1 

Global Change Biology: Bioenergy
ISSN: 1757-1693
EISSN: 1757-1707 

7 

5 

1019-1033 

10.1111/gcbb.12204 

WOS:000359384500009 

Cellulosic ethanol is widely believed to offer substantial environmental advantages over petroleum fuels and grain-based ethanol, particularly in reducing greenhouse gas emissions from transportation. The environmental impacts of biofuels are largely caused by precombustion activities, feedstock production and conversion facility operations. Life cycle analysis (LCA) is required to understand these impacts. This article describes a field-to-blending terminal LCA of cellulosic ethanol produced by biochemical conversion (hydrolysis and fermentation) using corn stover or switchgrass as feedstock. This LCA develops unique models for most elements of the biofuel production process and assigns environmental impact to different phases of production. More than 30 scenarios are evaluated, reflecting a range of feedstock, technology and scale options for near-term and future facilities. Cellulosic ethanol, as modeled here, has the potential to significantly reduce greenhouse gas (GHG) emissions compared to petroleum-based liquid transportation fuels, though substantial uncertainty exists. Most of the conservative scenarios estimate GHG emissions of approximately 45-60g carbon dioxide equivalent per MJ of delivered fuel (g CO(2)eMJ(-1)) without credit for coproducts, and 20-30g CO(2)eMJ(-1) when coproducts are considered. Under most scenarios, feedstock production, grinding and transport dominate the total GHG footprint. The most optimistic scenarios include sequestration of carbon in soil and have GHG emissions below zero g CO(2)eMJ(-1), while the most pessimistic have life-cycle GHG emissions higher than petroleum gasoline. Soil carbon changes are the greatest source of uncertainty, dominating all other sources of GHG emissions at the upper bound of their uncertainty. Many LCAs of biofuels are narrowly constrained to GHG emissions and energy; however, these narrow assessments may miss important environmental impacts. To ensure a more holistic assessment of environmental performance, a complete life cycle inventory, with over 1100 tracked material and energy flows for each scenario is provided in the online supplementary material for this article. 

biofuels; carbon intensity; cellulosic ethanol; climate change; corn stover; greenhouse gas; LCA; life cycle assessment; switchgrass