Page 290 - Materials Chemistry, Second Edition

A Comparison of Life Cycle Assessment Studies 281

although some researchers argued that it cannot be an accurate measure of energy
functions (Malça and Freire 2006; Shapouri et al. 2002) and it is not a measure of
environmental impacts also. When physical properties alone cannot be established
or used, allocation may be based on the economic value of the products although
price variation, subsidies, and market interferences could imply difficulties in its
implementation (Luo et al. 2009).
In a study of soybean-derived biodiesel, Huo et al. (2009) compared five
approaches to address the coproduct issues for various coproducts including pro-
tein products (such as soy meal), industrial feedstock (such as glycerin), and
energy products (such as propane fuel mix and heavy oils). These five approaches
includes the displacement approach, an energy-based allocation approach, a
market-value based allocation approach, hybrid approach I, which employs both
the displacement method (for soy meal and glycerin) and the allocation method
(for other energy coproducts) and hybrid approach II, which is exactly like hybrid
approach I except that it addresses soy meal with a market-value-based allocation
method. The results of the displacement approach are influenced significantly by
the extent of the energy and carbon intensity of the products chosen to be displaced
and argued that soy meal displacement could introduce uncertainties because soy
meal can displace many kinds of fodder and each fodder could have different
energy and carbon intensities. Huo and coworker suggested that when the choice is
between the displacement method and the allocation method, the displacement
method tends to be chosen if the uncertainties and difficulties associated with it are
solved, because it can reflect the energy use and emissions actually saved as a
result of the coproducts replacing other equivalent products. They also pointed out
that ‘‘energy-value-based allocation method is a favorable choice for a system in
which the value of all the primary product and coproducts can be determined on
the basis of their energy content, such as the production processes of renewable
fuels. If a non-energy coproduct is involved and there are difficulties associated
with using the displacement approach, the market-value-based allocation method
could be an acceptable choice, although the fluctuation of prices could affect the
results.’’ Huo et al. (2009) concluded that the integration of displacement method
and allocation method (hybrid approaches) could be the most reasonable choice of
allocation method for every coproduct. The results of the two hybrid approaches
were very close in terms of GHG emissions, indicating that the uncertainty
associated with using soy meal to displace soybeans would be in an acceptable
range. Reap et al. (2008b) observe that allocation failures hide or exaggerate
burdens associated with a product system, effectively biasing all downstream
results with an artifact of the analysis.
A number of scientific literatures are available which addresses the allocation
issue in LCA and describe the alternative approaches to allocation (Frischknecht
2000; Wang et al. 2004; Curran 2007; Luo et al. 2009). Wang (2005) showed
significant impact on overall energy and emission results of alternative allocation
methods for corn ethanol LCA, ranging from benefits relative to petroleum of
16–52 % in the case when the ethanol is made by a wet milling process. In another
study, Fergusson (2003) also found somewhat smaller (but nevertheless