(305b) Lifecycle Assessment and Policy: Implications of the Renewable Fuel Standard for Upper-Midwest Energy Supply

Lifecycle
Assessment and Policy: Implications of the Renewable Fuel Standard for

Upper-Midwest
Energy Supply

Michael Brodeur-Campbell¹, Jordan Klinger¹,
Kathleen Halvorsen^2,3, and David Shonnard^1,4

[1] Department of Chemical
Engineering, Michigan Technological University

[2] Department of Social
Sciences, Michigan Technological University

[3] School of Forest Resources
and Environmental Science, Michigan Technological University

[4] Director Sustainable Futures
Institute, Michigan Technological University

The use of biofuels derived from lignocellulosic biomass has received
significant public attention with Congressional policies such as the Energy
Policy Act of 2005 (EPAct), updated in the Energy
Independence and Security Act of 2007 (EISA) which included the Renewable Fuel
Standard (RFS).  The RFS mandates the
blending of ethanol and advanced / cellulosic biofuels into the U.S.
transportation fuel supply for each year until 2022.  The Renewable Fuel Standard has a lifecycle
perspective and contains lifecycle greenhouse gas emissions reduction
requirements (relative to petroleum gasoline) for the production of
biofuels.  Conventional ethanol derived
from corn starch must meet a 20% reduction level and is capped at 15 billion
gallons/yr.  ?Cellulosic? ethanol must
meet a 60% reduction standard and is expected to make up 16 billion gallons/yr.
by 2022.  ?Advanced? biofuel that meet a
50% reduction  must make up the remaining
5 billion gallons/yr mandated by 2022 (36 billion gallons/yr total ethanol).  In addition to demanding an accounting for both
direct and indirect land use change CO₂ emissions, the policy also
specifies several other environmental and social metrics to consider in
evaluating biofuel production. 
Environmental metrics specified include air
quality, water quantity and quality, wetlands and ecosystem health, and
wildlife habitat.  Other indirect effects
on society include energy security, commercial fuel production and
infrastructure, consumer fuel prices, job creation, agriculture impacts, rural
economic development, and future food prices.

While many studies have been performed on agricultural residues such as
corn stover (Sheehan, Aden et al. 2004, Hsu 2010) and wheat straw (Kabel, Bos et al. 2007), much
less attention has been given to woody feedstocks.  For this LCA, several regionally important
potential woody feedstocks are analyzed (hybrid poplar, hybrid willow, and
mixed hardwood logging residues) as well as two herbaceous feedstocks (switchgrass
monoculture, and a diverse prairie grass ecosystem).  This LCA is directly driven by the
requirements of the RFS and includes metrics for water and air quality, as well
as global warming potential.  Eutrophication
potential was chosen as the most important measure for water quality, as the
effects of fertilizer use in biomass cultivation generally dominate all
categories of water quality.  Particulate
matter emissions were chosen as the most important measure for air quality, as
this category has the greatest implication for human health. 

SimaPro 7.2 and the EcoInvent
database were used to model the process and assign environmental burdens.  A co-product credit is assigned to the
renewable electricity generated from the non-fermentable portion of the
biomass.  This electricity is modeled to
displace grid electricity at the regional mix for the states of Michigan,
Wisconsin, Minnesota, Iowa, and Illinois, which is derived approximately 70%
from coal-fired power plants.  Inputs and
outputs for the conversion were based on the National Renewable Energy
Laboratory Technical Report NREL/TP-510-32438 (Aden, Ruth, et al. 2002).  The ratio of fuel to electricity produced
from each feedstock was modified based on typical values for cellulose,
hemicellulose, lignin, ash, and extractives for each feedstock.  Table 1 below summarizes the results for
Global Warming Potential, Eutrophication Potential, and Particulate Matter
Emissions for the feedstocks analyzed.

Table
1: 
Summary of LCA Results for Cellulosic Ethanol

All fuel pathways analyzed meet 60% greenhouse
gas reduction requirements for a cellulosic biofuel, even before any co-product
credit is applied.  With co-product
credit some pathways result in net negative carbon emissions due to coal
displacement.  Eutrophication potential
is increased in all cases due to feedstock production activities; the highest
is for switchgrass which is the most fertilizer-intensive feedstock, while the
lowest is for multispecies prairie.   Particulate
emissions are reduced for all cases except logging residues, largely due to
avoided coal power.  Particulate matter
emissions for logging residues are high because of the low productivity per
acre and long transportation distances required to supply enough material for
conversion.

Future work will focus on refining our
feedstock conversion emission estimates using the ASPEN Plus process simulation
software, and on including land use change estimates for carbon flows.

References

Aden, A., M. Ruth, K. Ibsen, J. Jechura, K. Neeves, J. Sheehan,
B. Wallace, L. Montague, A. Slayton, and J. Lukas (2002).  Lignocellulosic Biomass to Ethanol Process
Design and Economics Utilizing Co-Current Dilute Acid Prehydrolysis
and Enzymatic Hydrolysis for Corn Stover.  National Renewable Energy
Laboratory, Golden, Colorado.

Hsu,
D., D. Inman, G.A. Heath, E.J. Wolfrum, M.K. Mann,
and A. Aden (2010). Life Cycle
Environmental Impacts of Selected U.S. Ethanol Production and Use Pathways in
2022.  Environmental Science &
Technology; 44, 5289-5297.

Kabel, M.A., Bos,
G., Zeevalking, J., Voragen,
A.G.J., Schols, H.A., (2007). Effect of pretreatment severity on xylan
solubility and enzymatic breakdown of the remaining cellulose from wheat straw.
Bioresource Technology; 98, 2034?2042.

Sheehan J, Aden A, Paustian K, Killian K,
Brenner J, Walsh M, et al. (2004) Energy
and environmental aspects of using corn stover for fuel ethanol.  Journal of Industrial Ecology;7(4):117e46.