Page 238 - Materials Chemistry, Second Edition

ACCOUNTING FOR ECOSYSTEM GOODS AND SERVICES 225

Emergy(sej) required to make
1kg 1,3-propanediol

Copper ore
■ Sand
Crushed stone
■ Gold ore
Hydropotential
■ Nuclear
m Coal
■ Natural gas
Crude oil

Fossil-based Bio-based

Figure 9.4 Emergy requirements based on Eco-LCA show an advantage to bio-based over
fossil-based systems, although, aggregating data into a single metric is risky (updated from
Urban & Bakshi 2009).

be directly compared for both feedstocks. However, because the bio-based
1,3-Propanediol will certainly have many ecological inputs, emergy will
likely be a more helpful basis of comparison. In addition, the comparison of
all the resources will also be adjusted for energy quality by accounting for all
of the solar emjoules (sej) contained in each resource. Since all resources, even
materials that are not forms of energy, will have a transformity that converts
their value and units to sej, this again gives a single unit that allows all of
the resources to be directly compared, as well as a value for the total emergy
associated with each feedstock that can be compared. Figure 9.4 above shows
the emergy required to make 1kg of 1,3-Propanediol from both the fossil
fuel-based and bio-based feedstocks. Only resources that make a significant
contribution to the products final emergy values have been included on this
graph.
As is expected, the majorly contributing resources to the fossil fuel-based
1,3-Propanediol are the fossil fuels coal, natural gas, and crude oil; nuclear
energy is also a large requirement due to nuclear energy's high transfor-
mity as well as the high power requirements to make the fossil fuel-based
1,3-Propanediol. The bio-based, on the other hand, has some power require-
ments as well, though most of its natural gas usage is actually due to needing
it for the chemical reactions in the processing. Looking at the emergy require-
ments of the two feedstocks, it appears that the bio-based 1,3-Propanediol
will be environmentally advantageous. However, any time the data is aggre-
gated into the single metric as done here, there is the risk that decisions may
be made blindly. Though it appears the emergy will be much lower for bio-
based 1,3-Propanediol, researchers should be sure to look at all the individual
resources to see if there are any vital resources that are higher for the bio-based
1,3-Propanediol.