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

Abstract

In this study, calcium oxide-magnetite (CaO-Fe₃O₄ NCs) nanocomposites 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 for 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.