Considering that the production of the second generation biofuels
from low quality feedstock (often contained water and FFA), the evaluation
of the catalytic behavior in the transesterification of vegetable oils
containing water and FFA was also examined. The M-CaO_100 catalyst
was used for conducting the reaction with the reaction time of 2.5 h,
methanol-to-oil molar ratio of 9 and catalyst loading of 7 wt.%.
In order to study the effect of water content on the catalysts, a certain
amount of water was added (0–4.0 wt.%) to palm oil. As illustrated
in Fig. 11a, when the water content was added from0.5 to 1.0 wt.%, the
increased FAME yield was found at the water content of 0.5 wt.%. This
suggested that a small amount of water could increase the reaction
rate due to the generation of more methoxide anions [26]. However,
further increase in the water content (from 1.0 to 4.0 wt.%) resulted in
the decrease of the FAME yield (from 96.0% to 82.1%). This was likely
due to the catalytic hydrolysis of FAME and/or glyceride to fatty acid
[41].
The FFA tolerance of catalysts was investigated with the addition of
0–4.0 wt.% FFA (palmitic acid) into the reaction mixture. As shown in
Fig. 11b, FFA has an obvious influence on the catalytic activity of the
M-CaO_100 catalyst. When the FFA content increased from 0 to
4.0 wt.%, the FAME yield decreased rapidly (from 96.2% to 48.0%). The