Environmental Engineering Reference
In-Depth Information
Picture 14.2 Sweet sorghum, a promising feedstock for the production of fuels and chemicals.
Courtesy University of Arkansas Division of Agriculture.
Currently first-generation feedstocks are available and they serve some purpose, but the
volume is not large enough to satisfy demand competitively with petroleum-based fuels and
chemicals. Second-generation feedstocks, even when useful, are also limited because not all
the crop residues can be harvested and transported out of the fields. A fraction of the residues
needs to be left on the ground as organic matter for the soil. Third-generation feedstocks are
the ones with potential to produce a big impact because they can have high yields and be
grown exclusively to produce fuels and chemicals. However, the massive use of these feed-
stocks is limited by the conversion technologies, which are not mature yet.
DOWNSIDES OF A BIOBASED ECONOMY
Production of fuels and chemicals from plants looks at first more benign than from petroleum-
based ones, but it also has serious drawbacks:
1.
The energy return on the investment (EROI). As was mentioned in Chapter 11, producing
energy takes an investment of energy, so for a fuel source to be feasible, it needs to gener-
ate more energy that what it is invested (EROI > 1). It is desirable to have an EROI of at
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