A suitable amount of palmitic acid and methanol was separately
pre-heated to desired temperature before being transferred to the
three-neck reactor (Fig. 1). Besides, the Amberlite IR-120 resin
used as solid catalyst was simultaneously added to this batch reactor
to initiate the esterification process. After preset reaction duration,
samples of biodiesel (methyl palmitate) were withdrawn from the
reacting mixture to determine the esterification efficiency by measuring
their acidity with a Metrohm 887 Titrino Plus auto-titrator
(Herisau, Switzerland). Esterification experiments were conducted
in triplicate to ensure good empirical reproducibility.
In brief, the conversion yield of palmitic acid to methyl palmitate at a
given reaction time was estimated from acidity of sample (mg KOH/g)
at the initial time (Ai) and at the desired time (Af) measured by an
auto-titration method [15]: