Snail shell derived magnetic nanocatalysts for biodiesel production: Process optimization through response surface methodology, kinetics, and thermodynamic studies

In this study, calcium oxide-magnetite (CaO-Fe₃O₄) nanocomposites (NCs) were synthesized from waste inorganic biomass (snail shells) using sequential calcination, hydration, and dehydration processes. The synthesized catalyst was thoroughly characterized using various techniques, including XRD, FTIR, TGA, SEM-EDS, BET, XPS, CO₂-TPD, VSM, and ICP-OES analysis and applied to the transesterification of soybean oil to produce biodiesel. The reaction was optimized using response surface methodology, achieving a high biodiesel yield of 97.7 ± 0.2 % (98.0 ± 0.4 % conversion). The quality of the biodiesel was confirmed by comparing its physicochemical properties with ASTM standards. The transesterification reaction followed pseudo-first-order kinetics with an activation energy of 42.5 kJ mol⁻¹. Furthermore, thermodynamic analysis showed that the process was endothermic (ΔH° = 39.13 kJ mol⁻¹) and non-spontaneous. The catalyst was reused for up to seven reaction cycles, and the nature of the reused catalyst after the seventh cycle was thoroughly examined later in the study.