Synthesis of biodiesel from various plant oils is realized by the
transesterification of triglycerides with methanol or by a reaction usually
defined as methanolysis. The usage of low-quality oils, such as waste
cooking oil (WCO), is followed by undesirable side reactions as a result of
the increased content of free fatty acids (FFA), and water. The presence of
FFA in WCO usually requires a pretreatment stage before subjecting it to
methanolysis. In the present work, heterogeneously catalyzed methanolysis of
WCO with and without pretreatment was investigated. Removal of FFA from WCO
was conducted by using only quicklime or with the addition of a small amount
of methanol (FFA to methanol = 1:3 molar ratio). The obtained results showed
that pretreatment of WCO with quicklime at 30?C after 1 h reduces the FFA
content by 72 %, while the adsorption capacity was determined to be 910 mg
g-1. The adsorptive pretreatment, as a simple operation, using low-cost
quicklime under mild conditions, had a positive effect on the
transesterification rate with CaO?ZnO as a catalyst, enabling the
achievement of over 96 % of biodiesel yield in only 15 min, compared to 1 h
without the pretreatment. Furthermore, pretreated WCO allows an increase in
repeated catalyst use and overall savings in the necessary amount of
catalyst. The present study showed that quicklime is an economic,
environmental-friendly, and sustainable material for FFA removal from WCO.