Acid-Catalyzed Esterification of Macauba Pulp (<i>Acrocomia aculeata</i>) and Brazil Nut (<i>Bertholletia excelsa</i>) Oils of High Acid Values over Mesoporous Silica Functionalized with Propyl Sulfonic Acid

Low-value vegetable oils of Macauba pulp (<i>Acrocomia aculeata</i>) and Brazil nut (<i>Bertholletia excelsa</i>) were esterified with methanol under heterogeneous acid catalysis conditions. The characterization of the raw vegetable oils revealed high free fatty acid and moisture content. The heterogeneous acid catalysts were prepared by co-condensation upon the grafting of propylsulfonic acid on MCM-41 (Pr-HSO₃/MCM-41) and SBA-15 (Pr-HSO₃/SBA-15) mesoporous silica materials. The catalysts were used in the esterification of the Macauba (<i>Acrocomia aculeata</i>) and Brazil nut (<i>Bertholletia excelsa</i>) oils. The yield of methyl esters reached up to 96%. The catalysts were easily recovered and tested for reuse. The catalyst grafted on the MCM-41 silica showed faster deactivation than the catalyst grafted on SBA-15, due to more severe leaching of the active phase. The results obtained during the esterification of the Macauba and Brazil nut oils indicated that the catalysts could be promising materials for producing biodiesel from raw materials containing high-acidity values.