Fig. 2. Single factor experiments of alkali-catalyzed esterification of WCO with glycerol. The esterification (%) of FFA–glycerol is affected by:
(a) Catalyst loading (200 °C, 3 h, and 1.1:1 molar ratio of glycerol to FFA);
(b) Mole ratio of glycerol to FFA (200 °C, 3 h, and 0.4 wt.% catalyst loading (WCO weight));
(c) Reaction temperature (1.1:1 molar ratio of glycerol to FFA, 3 h, and 0.4 wt.% catalyst loading);
(d) Reaction time (200 °C, 1.1:1 molar ratio of glycerol to FFA, and 0.4 wt.% catalyst loading). FFA: free fatty acid; WCO: waste cooking oil.