Page 213 - Materials Chemistry, Second Edition

EXERGY ANALYSIS AND ITS CONNECTION TO LIFE CYCLE ASSESSMENT 199

A comparison between exergy and life cycle analysis in assessing the sustain-
ability of the waste gas treatment options is also presented.
In line with the growing recognition that environmentally responsible chem-
istry is of great importance for achieving sustainable production, Van der Vorst
et ah (2009) apply exergetic life cycle assessment to two separation techniques
in the fine chemical and pharmaceutical industry Preparative supercritical
fluid chromatography and preparative high performance liquid chromatog-
raphy, which are widely used chiral separation techniques, are compared and
evaluated in terms of their integral resource consumption. It is concluded that
the most sustainable process based on integral resource consumption is pre-
parative high performance liquid chromatography.

8.4.5 Advantages of ExLCA

ExLCA is a useful tool, which has several advantages of over LCA. Some of
these advantages are as follows:

• Assessments using ExLCA consider not only inputs and emis-
sions, but also consider these quantities from the perspective of
exergy.
• LCA is often an "output side" method in that it focuses on emis-
sions and their impacts, whereas ExLCA focuses on both outputs
and inputs (Bakshi and Ukidwe, 2006). Complete mass, energy
and exergy balances are necessary for ExLCA.
• The depletion of natural resources such as mineral ores or energy
resources is measured directly as a loss of exergy via ExLCA
(Cornelissen and Hirs, 2002). Determining the depletion of natu-
ral resources is often a weaker point of LCA, since a distinction
is made between the commodity resources such as minerals and
energy resources such as fossil fuels. Resource depletion is not
determined in some LCA methods, often because of difficulties
in its calculation, and this approach can sometimes implicitly be
interpreted to imply that resource depletion is not a significant
environmental problem.
• Improving the efficiency of systems and processes, so as to
decrease their environmental impacts, is often aided more by
ExLCA than LCA, since all irreversibilities in subsystems and
subprocesses are addressed in ExLCA.

8.5 Case Study

The energy carrier hydrogen is expected by many to become an important fuel
that will help solve some energy challenges. Since its oxidation does not emit
greenhouse gases (GHGs), its use does not contribute significantly to climate
change over its life cycle provided it is derived from clean energy sources.