Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
biomass. Synthetic jet fuel from coal made by SASOL at the Secunda plant in South Africa
is being sold for jet aviation applications. Synthetic fuel represents the only currently
approved “drop-in” alternative fuel for the commercial aviation industry, in that it can be
applied directly to aviation applications without changes to existing aircraft engine or
frame design or the existing aviation fuel distribution system (Hileman et al., 2008).
Synthetic fuels are attractive as they have low concentrations of sulfur and aromatics and a
slightly higher hydrogen to carbon ratio. Use of these fuels in aviation application provide
significant reductions in sulfur and hydrocarbon emissions (Brown et al., 2008). Emissions
of particulate matter are reduced 50 to 90 percent while combustion CO2 emissions can
drop by two to four percent (Blackwell, 2007; Chevron, 2006). As noted earlier, however,
when life-cycle emissions are taken into consideration CO2 can increase significantly
depending upon the feedstock used in the process.
Alternatively, jet fuel can be created from animal fats, plant oils, sugars, and cellulose;
these products are often referred to as hydroprocessed renewable jet (HRJ) fuels and have
nearly the same weight, volume, and energy characteristics as petroleum-derived jet fuel.
HRJ fuels are seen as attractive for a variety of reasons, one of which being that when lifecycle
emissions are taken into consideration they can have a positive effect on greenhouse
gas emissions because all of the carbon in the finished fuel originated in the atmosphere as
CO2 which has been absorbed by plants that were turned into oils or fed to animals and
converted into fats (Syntroleum, 2009; Green Car Congress, 2007).
The U.S. Department of Defense’s Defense Advanced Research Projects Agency (DARPA)
in conjunction with the Energy and Environmental Research Center’s National Alternative
Fuels Center at the University of North Dakota are investigating a variety of affordable
alternatives to petroleum-based JP-8, include biofuels derived from agricultural (e.g., soy,
palm, canola, and coconut oil, and inedible oils such as jatropha and camelina and animal
fats) and aquacultural (i.e., algae) feedstock materials that are noncompetitive with food
sources. The goal of the BioFuels – Alternative Feedstocks study is to reduce the military’s
reliance on nonrenewable and imported sources of oil. DARPA is evaluating the
technological feasibility of developing fuels from these alternative feedstocks, as well as
the anticipated cost of these fuels (U.S. DOD, 2009). Similar studies currently are being
implemented in the private sector by aircraft and engine manufacture such as Boeing,
General Electric, and Rolls-Royce as well as many of the major airlines.
In order for bio HRJ fuels to meet stringent commercial aviation fuel standards, these fuels
need to be refined in a hydrotreatment process similar to that used for Hydrogenation–
Derived Renewable Diesel (HDRD). The higher costs for processing put HRJ fuels at a
higher price than HDRD. As jet fuel prices increase in the future HRJ fuels may be a
competitive option relative to existing petroleum products. Alternatively, cost impacts can
be reduced by blending biojet fuel with conventional jet fuel. In 2009, ASTM International
approved specification for 50 percent blend of FT fuel. Specification approval for 50
percent hydrotreated renewable jet fuel is expected in 2010.
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