Waste cooking oil (WCO) was used to produce biodiesel in a microtube reactor. First, the acid value of the
WCO was reduced from 3.96 mg KOH/g to less than 1 mg KOH/g via acid catalyzed esterification. The
effects of the methanol-to-WCO molar ratio (4.5:1–18:1), the H2SO4 concentration (0.5–2 wt.%), reaction
temperature (55–70 8C), and reaction time (5–20 s) were studied. The optimal conditions were 9:1
methanol-to-WCO molar ratio, 1 wt.% H2SO4, 65 8C and 5 s of reaction time. Triglycerides in the product
from the first step were transesterified with methanol and alkaline catalyst. Methyl ester content of the
biodiesel was 91.76%.