A Two-step Catalytic Production of Biodiesel from Waste Cooking Oil

Waste cooking oil (WCO) was used as a potential feedstock for biodiesel production. High levels of free fatty acids (9.85% w/w) in WCO made it an undesirable substrate for direct transesterification reaction. To solve this issue, a two-step process was implemented in this research. Firstly, esterification reaction was performed in presence of sulfuric acid as a common acid catalyst to reduce the amount of FFA to less than 1.5% w/w. The triglycerides (TGs) in WCO were transesterified with methanol catalyzed by potassium hydroxide in the second step of reaction. Several effective parameters were evaluated in terms of reaction temperature (323-363 K), reaction time (0.5-3 h) and catalyst concentration (0-5.52% w/w). The optimum reaction conditions were defined as the reaction temperature of 355 K, reaction time of 3 h and catalyst concentration of 3.68~ 4% w/w, in which maximum FFA conversion of 87 wt% was obtained. The biodiesel synthesis condition in the second stage was defined as the reaction temperature of 338 K, methanol/ WCO molar ratio of 6:1, KOH concentration of 1% w/w and reaction time of 90 min; under these conditions, maximum triglyceride (TG) conversion of 96.66 wt% was obtained.