Methyl ester production from cotton seed oil via catalytic transesterification process; characterization, fatty acids composition, kinetics, and thermodynamics study

Abstract

In this study, Cotton seed methyl ester (CSME) was produced from extracted Cotton seed oil (CSO) through transesterification process that involves two steps. The CSO obtained from solvent extraction was first esterified using an acid catalyst to obtain the FAME, which was then used in the based catalysed transesterification process that produced the CSME. The physicochemical properties and fatty acids composition of the extracted CSO and produced CSME were evaluated according to the ASTM approved standards. Also, the percentage conversion, activated energy, kinetics, and thermodynamics of the transesterification process were studied. The results also indicate that increase in time and temperature has a positive effect on the percentage conversion of CSO to CSME. The highest percentage conversion (95.48%) was achieved at 65 °C and 150 min. The reaction rate constants obtained for the irreversible pseudo first and second order models were within the range of 4.59×10-2 min-1 to 6.77×10-2 min-1 and 9.50×10-2 dm3mol-1min-1 to 2.27×10-1 dm3mol-1min-1, respectively. However, the R2 values indicate that the CSO transesterification reaction was best described by the irreversible pseudo second order model. The activation energy obtained was 18.98 kJ/mol and 43.17 kJ/mol for the pseudo first and second order models, respectively. ∆H, ∆S, and ∆G values for irreversible pseudo first and second orders models, are 13.89 KJ/mol, -0.158 KJ/mol, and 20.43 – 23.56 KJ/mol and 35.92 KJ/mol, -0.165 KJ/mol, and 85.21 – 88.31 KJ/mol, respectively. The cetane number, kinematic viscosity, calorific value, flash point, and acid value obtained for the CSME were 53.1, 4.81 mm2/s, 43,690 kJ/kg, 154 ℃, and 0.1 mg KOH/g oil, respectively. The CSME produced has physicochemical properties comparable to those of petroleum-derived diesel.