The synthesis of
biodiesel or fatty acid methyl esters (FAMEs)
from alternative feedstocks such as waste cooking oil through conventional
transesterification process is challenged by the presence of significant
amounts of free fatty acids (FFAs). Alternatively, these FFAs can
also serve as raw material for the synthesis of FAMEs through acid-catalyzed
esterification. In this study, we utilized graphene oxide (GO) as
a carbon-based heterogeneous acid catalyst in synergy with microwave
(MW) heating as a novel approach for an efficient synthesis of FAMEs
by esterification reaction at a shorter reaction time. Under this
process, 99.2% FAME was achieved at 3 min, methanol/oleic acid molar
ratio of 12, MW power of 200 W, and 1 wt % catalyst. It shows excellent
catalytic performance, which is more active than Amberlyst 15, sulfated
zirconia, and graphite oxide. Among the process variables investigated,
the ratio of methanol/oleic acid is the most important factor for
higher FAME yield. Additionally, the MW absorbing property of catalyst
is necessary for a successful synthesis. Therefore, the synergy of
MW and GO is a promising technique for a cost-competitive biodiesel
production from low-cost feedstocks containing high free fatty acids.