Sustainable biodiesel synthesis using bamboo leaves ash doped with Anser cygnoides eggshell derived CaO (BLA@SiO2-CaO) green catalyst: Characterization and optimization study

The increasing demand for sustainable and renewable energy sources has led to significant research in biodiesel production. This study explores the synthesis of castor biodiesel using a novel bamboo leaves ash (BLA@SiO₂) doped with swan goose (Anser cygnoides) eggshell derived CaO (BLA@SiO₂-CaO) as green catalyst. Anser cygnoides eggshells were calcinated at 900°C for 3 h, and doped with (BLA@SiO₂) via wet impregnation method at a mixing ratio of BLA@SiO₂:CaO – 1:2, 1:3, and 1:4 wt%. The catalysts were characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and energy dispersive X-ray to determine their structural and morphological properties. Box-Behnken design-response surface methodology was employed for optimizing biodiesel production process with four input factors viz. methanol: oil molar ratio, catalyst concentration, reaction temperature and reaction time. Results indicated that BLA@SiO₂-CaO catalyst exhibited excellent catalytic activity producing maximum biodiesel yield of 96.59 $\pm 0.95$% under the optimal conditions of 11.49:1 methanol to oil ratio, 5.27 wt% catalyst concentration, 60.24°C reaction temperature, and 1.54 h reaction time. The properties of biodiesel, including acid value (0.48 mg KOH/g), density (0.87 g/cm³), calorific value (40.5 MJ/kg), flash point (166°C), ester content (96.9 wt%), and kinematic viscosity (4.7 mm²/s) are found to be within the ASTM-D6751 and EN 14214 standard limits. The synthesized BLA@SiO₂-CaO catalyst could be reused for up to seven cycles with yield above 84.2 $\pm 1.1$%. This study highlights the potential of utilizing waste materials like bamboo leaves ash and swan goose eggshells as a cost-effective and eco-friendly catalyst in biodiesel production.