Brief
Overview
A
variety of fuels can be produced from biomass resources including
liquid fuels, such as, ethanol, methanol, biodiesel, Fischer-Tropsch
diesel and gasoline, and gaseous fuels, such as
hydrogen
and methane. Biofuels
are primarily used to fuel vehicles, but can also fuel engines
or fuel cells for electricity generation.
Fuels
Ethanol
Ethanol is
most commonly made by converting the starch from corn into sugar,
which is then converted into ethanol in a fermentation
process similar to brewing beer. Ethanol is the most widely used
biofuel today with 2008 capacity expected to be 12 billion gallons per
year based on starch crops, such as corn. Ethanol produced from
cellulosic biomass is currently the subject of extensive research,
development and demonstration efforts.
Biodiesel
Biodiesel is produced through a process in which organically
derived oils are combined with alcohol (ethanol or methanol)
in the presence of a catalyst to form ethyl or methyl ester.
The biomass-derived ethyl or methyl esters can be blended with
conventional diesel fuel or used as a neat fuel (100% biodiesel).
Biodiesel can be made from any vegetable oil, animal fats, waste
vegetable oils, or microalgae oils. Soybeans and Canola (rapeseed)
oils are the most common vegetable oils used today.
Bio-oil
A totally different process than that used for biodiesel production can be used
to convert biomass into a type of fuel similar to
diesel which is known as bio-oil. The
process, called fast or flash pyrolysis,
occurs when heating compact solid fuels at temperatures between 350 and 500
degrees Celsius for a very short period of time (less than 2 seconds). While
there are several fast pyrolysis technologies under development, there are
only
two
commercial
fast pyrolysis technologies as of 2008. The bio-oils currently produced are
suitable for use in boilers for electricity generation. There is currently
ongoing research and development to produce bioOil of sufficient quality
for transportation
applications.
Other
Hydrocarbon Biofuels
Biomass can be gasified to produce a synthesis gas composed primarily
of hydrogen and carbon monoxide, also called syngas or biosyngas.
Syngas produced today is used directly to generate heat and power
but several types of biofuels may be derived from syngas. Hydrogen
can be recovered from this syngas, or it can be catalytically
converted to methanol or ethanol. The gas can also be run through
a biological reactor to produce ethanol or can also be converted
using Fischer-Tropsch catalyst into a liquid stream with properties
similar to diesel fuel, called Fischer-Tropsch diesel. However,
all of these fuels can also be produced from natural gas using
a similar process.
A wide range
of single molecule biofuels or fuel additives can be made from
lignocellulosic biomass. Such production has the
advantage of being chemically
essentially the same as petroleum-based fuels. Thus modifications
to existing engines and fuel distribution infrastructure are not
required. Additional
information on green hydrocarbon fuels can be found on the Green
Hydrocarbon Biofuels page.
Source: U.S.
Department of Energy, Energy Efficiency and Renewable Energy,
http://www.eere.energy.gov/RE/bio_fuels.html
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