Biofuels Overview
A
variety of fuels can be produced from biomass resources including
liquid fuels, such as, ethanol, methanol, biodiesel, Fischer-Tropsch
diesel, 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
made by converting the carbohydrate from biomass 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 current capacity of 4.3 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.
BioOil
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 BioOil. The
process, called fast or flash pyrolysis,
occurs when heating compact solid fuels at temperatures between 350 and 500
degrees Celcius 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 2006. The BioOils currently produced are
suitable for use in boilers for electricity generation. Additional research
and development is needed to produce bioOil of sufficient quality for transportation
applications.
Biofuels from Synthesis Gas
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.
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.
Data on biofuels from synthesis gas are not currently included
in the Biomass Data Book.
Source: U.S.
Department of Energy, Energy Efficiency and Renewable Energy,
http://www.eere.energy.gov/RE/bio_fuels.html |
