Biodiesel, the monoalkyl esters of long chain fatty acids, is a
chemically modified fuel derived from various kinds of vegetable
oils and animal fats[2,5], which are composed primarily of high
molecular weight triglycerides. The viscosity of vegetable oils
and (especially) animal fats is higher than that of diesel fuel several
times over (about 11–17 times)[2]; and since viscosity affects the
flow properties of the fuel, such as spray atomization, consequent
vaporization, and air–fuel mixing in a diesel engine’s combustion
chamber. The use of high viscous oils as a fuel leads to adverse effects on the combustion process [5]. Hence, these oils must be
derivatized to be compatible with existing engines. One of the possible ways to achieve this purpose is conversion of large, branched
triglycerides into smaller, straight-chain molecules of monoalkyl
ester through a process called transesterification. This process
has been widely used to reduce the high viscosity of triglycerides
[2,7]. The transesterification of vegetable oil and fat can be represented by the general equation: