2.2. Esterification reaction
Esterification reactions were carried out in the presence of ChH2PW
at different reaction conditions. This reaction mixture was then irradiated
by microwave (A 2450 MHz microwave generator) under reflux
(65 °C) for the specified reaction time. After the esterification reaction
completed, the upper layer were esters and the excess alcohol and the
lower layer was the catalyst, which was recovered by decantation and
washing with methanol and removing water under a vacuum at 60 °C
for further use. The mixture was concentrated using a rotary evaporator
to remove the excess alcohol. The conversion of free fatty acid into ester
was calculated by measuring the acid value of the product and the yield
of ester was detected by gas chromatography (GC)