Parametric, kinetic, and thermodynamic studies of microwave-assisted esterification of Kusum oil

Abstract

In this research, non-edible Kusum oil was used to convert the free fatty acid into its methyl esters using a silicotungstic acid catalyst. The microwave as a heat source was used to fasten the rate of esterification of Kusum oil. The parametric study of the effect of methanol to oil molar ratio, catalyst amount, temperature, and time was carried out to obtain the reasonable conversion of free fatty acid. The study revealed that 9:1 molar ratio, 65 °C, 3.6 wt% catalyst, and 13 min of reaction time gave 92% free fatty acid (FFA) conversion. Further, the present study also estimates the kinetic and thermodynamic parameters of Kusum oil esterification. The kinetic study was performed at four temperatures with a pre-optimized 9:1 molar ratio of methanol to oil, 3.6 wt.% Silicotungstic acid for different time intervals. The kinetic study revealed that microwave-assisted acid-catalyzed esterification reaction is pseudo-first-order having activation energy 38.82 kJ.mol−1 and pre-exponential factor 219,037 min−1, respectively. The higher value of pre-exponential factor and lower activation energy in the kinetic study indicates the non-thermal effect associated with microwave heating. The rate constant and Gibbs’ free energy change at 65 °C was 0.224 min−1 and 98.89 kJ.mol−1. The values of Enthalpy and Entropy changes were 36.06 kJ.mol−1 and −0.185 kJ.mol−1.K − 1. It shows the reaction is non-spontaneous and endergonic by nature.