Considering data from literature reviews, the concentration of
KOH was tested in a range of 0.5–1.5 wt% of WCO. Fig. 2 shows
the effect of concentration of KOH on the conversion at the methanol/WCO ratio of 8:1. Increasing KOH concentration from 0.5 wt%
to 0.75 wt% increased the conversion. It was 82% and 90% at
0.5 wt% KOH and 0.75 wt% KOH, respectively during 120 min.
However, the conversion reduced to 75% in the case of
1.5 wt% KOH. This could be explained by the fact that the formation of soap hindered the separation of the methyl ester phase during the washing step. The soap particles formed emulsions with
water, which resulted in increased viscosity. This phenomenon
did not occur at low KOH concentrations. As a consequence, the
yields of biodiesel were low for the cases of 1 wt% and
1.5 wt% KOH.