Page 235 - Materials Chemistry, Second Edition

222 LIFE CYCLE ASSESSMENT HANDBOOK

with both the aggregated metrics and original results available (Zhang, Baral,
& Bakshi, 2010).

9.4 Case Study Comparing Process-Based and Hybrid
Studies Based on EIO-LCA and Eco-LCA

To demonstrate the strengths and weaknesses of the various LCA methods,
a case study is done using process-based LCA and hybrid studies based on
EIO-LCA and Eco-LCA. This case study looks at manufacturing 1,3-propane-
diol from both fossil fuel and biomass sources. The fossil fuel route looks at the
reaction of syngas with ethylene oxide over a catalyst to form the 1,3-propane-
diol. The biomass source uses corn glucose, which is fermented by a geneti-
cally modified strain of E. coli. These processes were originally investigated
by Urban and Bakshi using a process LCA and hybrid studies using both EIO-
LCA and Eco-LCA; however, these hybrid studies were based on the 1997
Economic Input-Output model, so different conclusions may arise from the
updated study. In addition, in the previous study, the carbon and nitrogen foot-
prints were not yet a part of Eco-LCA (Urban & Bakshi, 1,3-Propanediol from
Fossils versus Biomass: A Life Cycle Evaluation of Emissions and Ecological
Resources, 2009).
The process-based LCA will give results based on a very specific process,
using a chosen boundary with the most important contributors being part of
the system. This will be a valuable methodology to use when looking at one
specific way to make the 1,3-propanediol because it will be precisely tailored
to that system. However, the hybrid studies will be able to consider more com-
plete information about the supporting industries, which may give results
that are more pertinent. In this case study, since the EIO-LCA and Eco-LCA
are both based on the 2002 Economic Input-Output model from the Bureau
of Economic Analysis, we expect their results in categories common to both
methods to be quite similar. However, the Eco-LCA model focuses more on the
different ecosystem goods and services that fuel our economy, so the Eco-LCA
results will give much more information on the specific resources used than
the EIO-LCA will. Though to begin, we will compare a resource that is con-
tained in all of the various forms of analysis: non-renewable fossil fuel energy
consumption. Following is a graph showing the amount of fossil fuel con-
sumption for 1kg of fossil fuel-based and bio-based 1,3-propanediol (Urban &
Bakshi, 1,3-Propanediol from Fossils versus Biomass: A Life Cycle Evaluation
of Emissions and Ecological Resources, 2009).
For the fossil-based 1,3-propanediol, the EIO-LCA and Eco-LCA have sig-
nificantly lower values than the Process LCA (see Figure 9.1). This is likely
due to the aggregation issues that arise with the EIO and Eco-LCA. The
fact that these models look at industries as a whole instead of individual
processes within a sector may be the source of the difference. The sectors
that contribute to the manufacturing of 1,3-propanediol may also contain
other commodities that require less fossil fuel energy. This would then cause