Waste cooking oils are combination of saturated and unsaturated
monocarboxylic acids with the trihydric alcohol glyceride.
During the transesterification process with the help of catalyst,
the triglycerides convert to diglycerides, then it is followed by
the diglycerides to monoglycerides conversion and then finally to
glycerol. In each step, one methyl ester molecule is produced from
each glyceride [33]. The waste cooking oil had a high free fatty acid
value (4.43 mg/g) which will lead to excessive soap formation.
The soap formation process is not preferred due to it will lower
the yield of esters and make the separation of esters difficult