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

Abstract

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.