A novel biodiesel production process using waste cooking oil (WCO) as feedstock was developed in this work.
Free fatty acids (FFAs) from WCO were esterified by crude glycerol catalyzed by NaOH, which lowered the
content of free fatty acids of WCO. The conversion of FFA in the WCO (acid value: 124.9 mg KOH/g) to
acylglycerols is 99.6% under the optimal conditions (1.4:1 molar ratio of glycerol to FFA, 4 h, 210 °C, catalyst
loading 0.5 wt.% based on WCO weight). After the transesterification of esterified WCO with methanol catalyzed
by NaOH, the yield of thefinal product is 93.1 wt.% with 98.6 wt.% of fatty acid methyl ester (FAME). The crude
glycerol and the catalyst from transesterification were recycled as reactant for esterification during the biodiesel
production. Soap formed from the subsequent processes maintained a high catalyzing activity for FFA
esterification after being recycled for 13 times. This new glycerol esterification process using alkali (soap) catalyst
provides a promising solution to convert feedstock with high FFA levels to biodiesel. This biodiesel production
process has distinct advantages compared with traditional two-step methods, including lower cost of catalyst
for both esterification and transesterification processes, less energy consumption for methanol recovery,
recycling of the glycerol byproduct and catalyst (soap), and no requirement of anti-corrosive equipment