Development of CaO/Al2O3 bifunctional catalyst for biodiesel production from jatropha oil: optimization and kinetic study

Biodiesel production from non-edible Jatropha curcas oil, which have high free fatty acid (FFA) content, presents technical challenges due to soap formation during conventional base-catalyzed transesterification. This often necessitates a costly and time-consuming acid pretreatment. To address this, the study developed a bifunctional heterogeneous calcium-/aluminum oxide (CaO/Al 2 O 3 ) catalyst synthesized from calcined snail shells (SS) and impregnated with alumina. The catalyst enables direct transesterification of high-FFA jatropha oil, thereby simplifying the process and reducing wastage. Optimization of the transesterification parameters using central composite design (CCD) revealed an optimal biodiesel yield of 93.4% at 64.3°C, 2.65 h, 2.29% catalyst loading and a methanol-to-oil molar ratio of 0.396. Catalyst characterization using X-ray diffraction (XRD) analysis of a raw (uncalcined) sample, showed that the dominant component was aragonite or calcium carbonate (CaCO 3 ) at 86.6%, after 900°C calcination. Based on the XRD trend, a shift from aragonite to CaO (quicklime) as the dominant phase at 85.9% occured. SEM images of CaO before impregnation showed a highly porous structure with fine, loosely aggregated particles. After impregnating the CaO with Al 2 O 3 , the structure appeared denser and more compact, with the presence of larger cluster or agglomerates resulting from coating or filling pores by Al 2 O 3 . Structural changes in the catalyst due to Al 2 O 3 impregnation are reflected in the Fourier Transform Infrared (FTIR) data, a validation of the formation of a more stable and potentially more active CaO/Al 2 O 3 composite catalyst. Kinetic studies showed the reaction followed second-order kinetics with an activation energy of 37.54 kJ/mol. The catalyst retained over 85% yield after regenerative studies. From the foregone, the potential of CaO/Al 2 O 3 as an efficient, cost-effective, and sustainable catalyst for biodiesel production from high FFA feedstock is described as solid.