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

Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
modification to the vehicle engine, distribution infrastructure, and fueling infrastructure.
FT fuels also are considered ultralow sulfur.
Biobutanol
Butanol derived from biomass feedstock is referred to as biobutanol. Like ethanol, butanol
is suitable for blending with gasoline. The energy content of butanol is higher than
ethanol but lower than gasoline. EPA considers gasoline blends with up to 11.5 percent
butanol to be operationally similar to pure gasoline (AFDC, 2009a). Testing of higher
concentrations of biobutanol in current vehicles has been limited, so it is uncertain what
upper limit of biobutanol blend can be used without requiring vehicle modifications.
Although butanol is generally being considered as a gasoline blend component, a
preliminary study by Argonne National Laboratory (cited at the Green Car Congress web
site) has shown that use of butanol as a blending agent in diesel fuel reduces emissions of
particulate matter without significantly increasing NOx.
Biobutanol also does not cause corrosion and water contamination problems as does
ethanol, so biobutanol could likely use existing gasoline infrastructure for distribution.
Biobutanol would not require new or modified pipelines, blending facilities, storage tanks,
or retail dispensing pumps. In addition, relatively minor modifications are required to
adapt existing ethanol facilities to produce butanol.
Processes to produce butanol by fermentation of biomass have existed for many years, but
these processes have been more expensive than production of petrochemicals. However,
there are several efforts currently underway to produce biobutanol more efficiently and
economically. Nevertheless, the long-term production potential and costs for biobutanol
remain highly uncertain at this early stage of development (Lammers, 2008). Furthermore,
production of biobutanol results in significant volumes of acetone as a byproduct, and it is
not clear what would be done with this acetone if biobutanol were produced on a large
scale (Smith, 2009).
Biomass-to-Liquids (BTL)
Most BTL processes today are either a) gas-to-liquid processes, in which biomass is first
converted into a gas, then to a liquid, or b) pyrolysis processes in which biomass is
decomposed in the absence of oxygen to produce a liquid oil. In the gas-to-liquid process,
biomass is heated with insufficient oxygen for complete combustion, producing synthesis
gas (syngas) composed of carbon monoxide and hydrogen. There are a variety of
commercial processes that can be used to convert syngas into useful products, including
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