Design of Activated Bentonite-Based Catalysts for the Esterification of Residual Free Fatty Acids From Palm Oil

Bentonite, a readily available and abundant natural mineral, serves as a cost-effective catalyst for esterifying free fatty acids (FFAs). In this study, an economical method was developed to enhance the catalytic activity of Chocolate bentonite (Ca-CB) from Paraíba, Brazil, for the methyl esterification of distilled deodorized palm oil (DDPO), an agroindustrial by-product containing approximately 84% FFAs. Raw bentonite and activated material were characterized using various techniques, including nitrogen physisorption, X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA)/differential thermogravimetry (DTG), scanning electron microscopy (SEM), and acid-base titration.The highest conversion rate of 93% was achieved using H-Ca-CB in the esterification of DDPO, surpassing H-Na-Ca-CB (91%) and the commercially available K-10 catalyst (81%). Furthermore, H-Ca-CB maintained superior catalytic activity (over 75%) even after four reuse cycles, outperforming autocatalysis (34%). Kinetic studies of the transesterification process indicated that the pseudo-first-order model was the most suitable, with an activation energy of 27.40kJmol–1. These findings underscore the effectiveness of natural bentonite in catalytic synthesis, attributed to its enhanced textural properties and surface acidity.