Environmental Engineering Reference
In-Depth Information
FIGURE 5.2
Stored corn biomass feedstock.
categorized as first-generation or second-generation feedstocks. First-generation
feedstocks include those that are already widely grown and used for some form of
bioenergy or biofuel production, which means that food vs. fuel conflicts could arise.
First-generation feedstocks include sugars (sugar beets, sugar cane, sugar palm,
sweet sorghum, and
Nypa
palm), starches (cassava, corn, milo, sorghum, sweet
potato, and wheat), waste feedstocks such as whey and citrus peels, and oils and fats
(coconut oil, oil palm, rapeseed, soy beans sunflower seed, castor beans,
Jatropha
,
jojoba, karanj, waste vegetable oil, and animal fat). Second-generation feedstocks
include crops that offer high potential yields of biofuels but are not widely cultivated
or not cultivated as an energy crop. Examples are cellulosic feedstocks or conven-
tional crops such as
Miscanthus
grasses, prairie grass and switchgrass, and willow
and hybrid poplar trees. Algae and halophytes (saltwater plants) are other second-
generation feedstocks.
Currently, a majority of the ethanol produced in the United States is made from
corn or other starch-based crops (see Figure 5.2). The current focus, however, is
on the development of cellulosic feedstocks—non-grain, non-food-based feedstocks
such as switchgrass, corn stover, and wood material—and on technologies to con-
vert cellulosic material into transportation fuels and other products. Using cellulosic
feedstocks not only can alleviate the potential concern of diverting food crops to
produce fuel but can also offers a variety of environmental benefits (EERE, 2008).
Because such a wide variety of cellulosic feedstocks can be used for energy pro-
duction, potential feedstocks are grouped into categories—or pathways.
Figure 5.3
shows some of the specific feedstocks in each of these areas.
