Sustainable biodiesel production from cottonseed oil using a nickel-doped eggshell heterogeneous catalyst optimized via response surface methodology.

This study presents a sustainable and low-cost approach to biodiesel production using non-edible cottonseed oil and a novel nickel-doped chicken eggshell-derived catalyst. The catalyst was synthesized via nickel impregnation followed by calcination at 900 °C to facilitate the decomposition of CaCO₃ into catalytically active CaO and promote nickel oxide formation for enhanced surface reactivity. Process optimization using Response Surface Methodology (RSM) resulted in a maximum fatty acid methyl ester (FAME) yield of 98.01% under optimal conditions. These included a reaction temperature of 62 °C, a 12:1 methanol-to-oil molar ratio, 4 wt% catalyst loading, and 117 min reaction time. This performance surpassed the 96.3% yield obtained using undoped CaO. Characterization revealed high crystallinity (68.2%) and a porous morphology, contributing to improved catalytic performance and reusability. The cottonseed oil feedstock exhibited favorable properties, including low moisture content (1.2%) and high volatility (94.4%). FTIR and GC-MS analyses confirmed successful transesterification, with the biodiesel rich in linoleic acid (50.5%) and meeting ASTM fuel standards (cetane number 53.75, viscosity 4.96 mm²/s). These findings demonstrate a scalable, environmentally friendly biodiesel production route that leverages waste-derived materials, supporting circular economy goals and sustainable energy strategies in resource-constrained regions.