Biodiesel Defined
The use of vegetable oil as a fuel source in
diesel engines is as old as the diesel engine
itself. However, the demand to develop and
utilize plant oils and animal fats as biodiesel
fuels has been limited until recently. The
technical definition of biodiesel is: “The
mono alkyl esters of long fatty acids derived
from renewable lipid feedstock such as
vegetable oils or animal fats, for use in compression
ignition (diesel) engines” (National
Biodiesel Board, 1996). In simple terms,
biodiesel is a renewable fuel manufactured
from methanol and vegetable oil, animal fats,
and recycled cooking fats (U.S. Department
of Energy, 2006).
The term “biodiesel” itself is often misrepresented
and misused. Biodiesel only refers
to 100% pure fuel (B100) that meets the
definition above and specific standards given
by the American Society of Testing and
Materials (ASTM) International (D 6751)
. However, it is often used to describe
blends of biodiesel with petroleum diesel.
Such blends are generally referred to as
“B2,” “B5,” “B20,” etc., where the number
indicates the percent of biodiesel used.
The most common method to produce
biodiesel is through a process called
“transesterification,” which involves
altering the chemical properties of the
oil by using methanol (Fangrui and
Hanna, 1998). Transesterification of plant
oils with methanol is a relatively simple
process that yields high conversions with
only glycerin as a byproduct.