Surachai Jansri, Gumpon Prateepchaikul, and Sukritthira B. Ratanawilai, “Acid-Catalyzed Esterification: A Technique for Reducing High Free Fatty Acid in Mixed Crude Palm Oil”, Agr. Nat. Resour., vol. 41, no. 3, pp. 555–560, Sep. 2007.