Acid-catalyzed esterification and kinetics of Zanthoxylum bungeanum seed oil for biodiesel preparation

We developed a method to reduce the acid value of crude Zanthoxylum bungeanum seed oil (ZSO) with high free fatty acids. The acid value of ZSO was reduced from 56.23 mg KOH/g to 1.56 mg KOH/g by using one-step, acid-catalyzed esterification under the following optimum conditions: methanol-to-oil molar ratio of 30: 1; 1.5% H2SO4; temperature of 60 degrees C; and a reaction time of 120 min. The variation analysis of the orthogonal tests reveals the following sequence of different factors that contribute to esterification: mole ratio of methanol to ZSO > w (catalyst) > reaction temperature > reaction time. Results show that the mole ratio of methanol to ZSO has a significant influence on esterification and deacidification. The esterification kinetics reveals that the acid-catalyzed esterification of ZSO to methanol is a two-step reaction. The dynamics equation is obtained and the activation energy (Ea) is 9542 J/mol at 60 degrees C. The work laid a good foundation for subsequent biodiesel preparation.