Transesterifying Ricinus communis, Brassica napus, and waste soybean oil over calcareous heterogeneous catalyst for biodiesel production: A comparative assessment

Mounting environmental repercussions stemming from persistent fossil fuel reliance have catalyzed the exploration of renewable energy alternatives, with biodiesel emerging as a prominent alternative. This work aims to validate a low-cost, waste-derived calcium oxide (CaO) catalyst (from postconsumer eggshells) for scalable biodiesel production across castor, Brassica napus, and waste soybean oils (WSO) by optimizing transesterification. Despite the well-documented catalytic efficacy of nano-structured heterogeneous systems, their synthesis complexity and elevated cost structures frequently inhibit industrial-scale translation. To circumvent these limitations, this study employs CaO derived from postconsumer eggshells, an agro-waste source, as an economical, bio-originated catalyst for transesterification. Comprehensive characterization of the catalysts was carried out using Scanning Electron Microscope (SEM), energy-dispersive X-ray spectroscopy, Fourier transform infrared (FTIR), X-ray diffraction, Brunauer Emmett Teller (BET), and particle size analysis. Under optimized reaction conditions (12:1 methanol-to-oil molar ratio, 5 wt% catalyst loading, 65 °C, and 2.25 h), conversion efficiencies of 90.53% (castor oil [CO]), 89.05% (Brassica napus oil [BN]), and 92.14% (WSO) were achieved, confirming the catalyst’s adaptability and robustness across diverse lipid matrices. FTIR analysis substantiated successful ester formation. The fuel properties conformed to American Society for Testing and Materials (ASTM) standards, while cost estimations revealed favorable economics at $1.10/L (CO), $1.04/L (BN), and $0.21/L (WSO). These outcomes underscore a scalable, low-cost approach for biodiesel synthesis from readily available agro-based residues, with strong implications for decentralized, resource-constrained production landscapes.