Biodiesel production from spent vegetable oil with Al2O3 and Fe2O3-biobased heterogenous nanocatalysts: Comparative and optimization studies

A waste-to-wealth approach was adopted in this study to establish an efficient, economically viable, and environmentally sustainable process for producing biodiesel from Spent Vegetable Oil (SVO). This involved the synthesis and calcination at 800 °C of aluminum and iron oxide snail shell-based catalysts (F2O3-SS and Al2O3-SS) using the wet-impregnation method. The catalysts were characterized using FTIR, XRD, and SEM-EDS, and then used in the transesterification of SVO to produce biodiesel. Optimization was performed using three-factor Box-Behnken Design (BBD): reaction time, catalyst concentration, and temperature. After extensive physicochemical study, FTIR and GC–MS analyses were further carried out on the produced biodiesel. The XRD results showed crystalline composites with an average lattice parameter of 8.5583 Å (Fe2O3-SS) and 7.4813 Å (Al2O3-SS). EDX and FTIR confirmed surface modifications with the formation of metal oxide (Me-O) at 543 cm−1 (Al-O) and 613 cm−1 (Fe-O). SEM micrographs show flower-like and spherical-shaped nanocomposites of F2O3-SS (162 nm) and Al2O3-SS (660 nm), respectively. Under optimal transesterification conditions of 120 min, 1.0 wt%, and 90 °C, biodiesel yields of 94.23 ± 0.50 and 91.94 ± 0.21 % were recorded for both Al2O3-SS and F2O3-SS, respectively. FTIR analysis corroborated the biodiesel production, with a distinctive C-O-C ester stretch at 1021 cm−1 for both catalysts. The produced biodiesel recorded a low moisture content and specific gravity values of 0.03 % and 0.8011 kg/m3 for Al2O3-SS, 0.02 % and 0.8042 kg/m3 for Fe2O3-SS. GC–MS analysis shows hexadecanoic acid, 15-methyl-, methyl ester as the predominant component, constituting 29.87 % and 25.34 % for Al2O3-SS and F2O3-SS, respectively. Furthermore, activation energy (Ea) values of 50.42 and a pre-exponential factor (A) of 2.2 × 105 were recorded for Al2O3-SS while 45.94 kJ/mol and 6.2 × 104 were recorded for Ea and A, respectively for Fe2O3-SS. The outcomes of this research reveal the efficacy of utilizing aluminum and iron oxide snail shell-based nanocatalysts for biodiesel production from spent vegetable oil. However, future studies should focus on evaluating their long-term stability, assessing their environmental impact, and identifying potential applications in large-scale biodiesel production.