Variables Affecting Biodiesel Production from Zanthoxylum bungeanum Seed Oil with High Free Fatty Acids

The Zanthoxylum bungeanum seed oil (ZSO) having high free fatty acids was successfully transformed into biodiesel by add-catalyzed esterification and alkali-catalyzed transesterification and high conversion to biodiesel was obtained in a short time compared to acid-catalyzed transesterification. Methanol-to-oil molar ratio, catalyst amount, and reaction time were found to clearly affect the ferric sulfate-catalyzed esterification of ZSO. The acid value of ZSO was reduced to less than 2 mg of KOH/g with a methanol-to-oil molar ratio of 16:1, catalyst amount of 2%, and reaction time of 3 h, following transesterification using an alkaline catalyst. The conversion to biodiesel by potassium hydroxide-catalyzed transesterification was achieved above 98% under optimum conditions: a methanol-to-oil molar ratio of 6:1, catalyst amount of 1.5%, reaction time of 60 min, and reaction temperature of 60 degrees C. The biodiesel production process was also confirmed by H-1 NMR and FTIR.