Abstract

Esterification of higher free fatty acids content by using a photo-catalyst has recently been proved as the most efficient method for the pretreatment of non-edible oil to synthesize biodiesel.

Methods: In the current study, mechanistic details of photo-catalyzed esterification reaction for four different fatty acids through density functional theory (DFT) calculations are explored and compared with un-catalyzed esterification reaction.

Results: Revealed that the presence of photo-catalyst lowers the activation barrier and the structure of fatty acid has no significant effect on its reactivity. Thermodynamic data also revealed that the presence of photo-catalyst lowered the activation energy from 51.67 kcal/mol to 0.7495 kcal/mol. Furthermore, Gibbs free energy changes (Δ_rG_m Ø) and molar enthalpy changes (Δ_rH_m Ø) of the photo-catalyzed esterification reaction are negative, indicating that it is a spontaneous exothermic reaction. On the other hand, free fatty acids esterification in the absence of a catalyst is a kinetically unfavorable process with positive values of Δ_rG_m Ø and Δ_rH_m Ø.

Conclusion: Our findings theoretically clarify the mechanism of the photo-catalyzed esterification reaction of FFA present in non-edible oil, which facilitates the process of biodiesel production.

Keywords: Esterification, density functional theory (DFT), reaction mechanism, soaf nut, biodiesel, photocatalyst.