Sequential Acid-Catalyzed Esterification and Base-Catalyzed Transesterification of Babassu (Attalea speciosa Mart. Ex Spreng.) and Pequi (Caryocar brasiliense Camb.) Oils of High Acid Values Over Functionalized Mesoporous Silicas

Abstract

In this work Babassu (Attalea speciosa Mart. Ex Spreng.) and Pequi (Caryocar brasiliense camb.) vegetable oils of high acid values were transformed in the respective methyl esters, through sequential acid-catalyzed esterification and base-catalyzed transesterification over functionalized mesoporous heterogeneous catalysts. The vegetable oils were firstly esterified with methanol over SBA-15 functionalized with propylsulfonic acid (Pr-HSO3/SBA-15) or K-10 Montmorillonite. The oil to methanol molar ratio, temperature, catalyst loading, and time were varied to assess the best conversion of the free fatty acids. The esterification with Pr-HSO3/SBA-15 catalyst yielded 94% and 83% in the esters for the Babassu and Pequi oils, respectively, at the best reaction conditions studied. K-10 Montmorillonite showed a poorer performance in the esterification, yielding 70% of methyl esters for the Babassu oil. The Pr-HSO3/SBA-15 acid catalyst showed negligible loss of activity for three consecutive reuses, whereas K-10 is significantly poisoned upon the first use. These results may be explained by the higher acidity of the hybrid catalyst. The esterified oils were subject to transesterification with methanol in the presence of MCM-41 mesoporous silica grafted with 1,5,7-triazabicyclo [4,4,0] dec-5-ene (TBD/MCM-41) basic catalyst. At the best conditions studied, the esterified Pequi oil achieved 89% conversion in the methyl esters. The results may be explained by the relatively low incorporation of the organic base on the silica support. The sequential esterification and transesterification of Babassu and Pequi oils over functionalized silica heterogeneous catalysts may be a sustainable alternative to the production of biodiesel in remote regions.