Sustainable valorization of dual-waste-derived CaO-functionalized MCM-41 catalyst for low-temperature biodiesel production from waste cooking oil: A comprehensive kinetic and thermodynamic investigation

The transition to sustainable fuels demands not only renewable feedstocks but also efficient and low-cost catalysts derived from waste resources. Here, we report a novel waste-derived mesoporous CaO-MCM-41 catalyst, with calcium oxide sourced from snail shells and MCM-41 silica derived from sugarcane bagasse ash. Comprehensive characterization (XRD, FT-IR, Raman, CO2-TPD, SEM, TEM, TGA, and XPS) confirmed the successful incorporation of CaO into the mesostructured support, providing high basicity, uniform dispersion, and structural stability. The optimized 30 wt% CaO-MCM-41 catalyst achieved a biodiesel yield of 97.2 % from waste cooking oil under mild transesterification conditions (3 wt% catalyst, 45 °C, 7:1 methanol-to-oil ratio, 150 min). Kinetic analysis indicated a low activation energy (Ea. = 36.88 kJ mol−1) with strong model conformity (R2 = 0.976), while thermodynamic factors (ΔH# = +32.09 kJ mol−1, ΔS# = −175.88 J mol−1 K−1) suggested an endothermic, associative pathway. Importantly, the catalyst demonstrated excellent reusability, retaining high activity over six cycles with negligible Ca leaching as confirmed by ICP-OES. The produced biodiesel complied with ASTM D6751 and EN 14214 specifications, affirming its commercial viability. This study highlights a scalable, eco-friendly, and recyclable catalytic system that integrates green chemistry principles with high efficiency, offering a promising route to low-cost biodiesel production.