The traditional way to produce biodiesel is by catalytic transesterification of vegetable oil with an alcohol to yield fatty acid alkyl esters and
glycerol. The alkali-catalyzed transesterification is considered to be
efficient and can achieve high purity and yield, but it requires feedstock
with high purity. For example, Freedman et al. studied the influence of
free fatty acid (FFA) in the biodiesel production and found that the
acid value of the feedstock should be less than 1.0 mg KOH/g, or the
yield of FAME would be reduced due to the deactivation of the catalyst
and hydrolysis of triacylglycerol caused by the soap formed