ABSTRACT

Biodiesel produced from waste cooking oil (WCO) is increasingly becoming a cheap and viable option to address the food vs fuel debate in biodiesel production. The kinetic and thermodynamic studies for the transesterification of waste cooking oil over a bio-based bifunctional catalyst (BBFC) obtained from eggshells and fuming sulphuric acid are presented in this research. BBFC was synthesized via impregnation of fuming sulphuric acid and calcined eggshell on carbonaceous support derived from rubber seed shells. The catalyst was characterized using Brunuar-Emmett Teller (BET) analysis, scanning electron microscopy (SEM), and Fourier-transform infrared (FTIR) spectroscopy. The catalyst's distinguishing feature is that it simultaneously facilitates esterification and transesterification reactions. The experimental data obtained were fitted into the pseudo-first-order kinetic model and the unimolecular second-order kinetic model and from the analysis of the correlation coefficient (R²) of both plots, it was found that the pseudo-first-order model best describes the reaction. The minimum amount of energy necessary to activate the molecules to undergo a chemical reaction and the frequency factor was calculated as 35.53 kJ/mol and 46.42 (min⁻¹), respectively. The curve fitting of the pseudo-first-order reaction gave an R² value of 0.991. Thermodynamic parameters such as change in enthalpy (ΔH), change in entropy (ΔS), and the change in Gibbs free energy (ΔG) were also computed to determine the nature of the transesterification process. The value of  was estimated as and that of .  was calculated for the three reaction temperatures. At 45°C (318K), 55°C(328K) and 65°C(338K) were calculated as; ,   respectively. The positive value of ΔG confirmed that the reaction was unspontaneous and endergonic.