Esterification of Khaya senegalensis seed oil with a solid heterogeneous acid catalyst: Modeling, optimization, kinetic and thermodynamic studies

Abstract

The current study investigated the esterification of Khaya senegalensis seed oil (KSSO) with a high free fatty acid (FFA) using ferric sulfate (Fe 2 (SO 4 ) 3 ) as a solid heterogeneous acid catalyst. Taguchi design approach was applied in modeling and optimizing the input variables to obtain the minimum %FFA for the KSSO esterification process. Besides modeling and optimization, the kinetic and thermodynamic studies of the process were carried out to obtain pertinent data required for reactor design. The optimum values with the minimum %FFA (0.49) for the esterification process are a temperature of 60 °C, methanol-to-KSSO ratio of 15:1, ferric sulfate dosage of 9 wt%, and time of 60 min. The reaction of the triglycerides in the KSSO with methanol showed that it followed first-order kinetics. The pre-exponential factor ( A ), activation energy ( E a ), and reaction rate constant ( k ) for the reaction are 37.73 min -1 , 18.11 kJ/mol, and 0.0554 min -1 , respectively, at a temperature of 60 °C, indicating that the esterification process proceeded at a fast rate. The thermodynamic properties determined for the process are Δ S § (entropy), Δ H § (enthalpy), and Δ G § (Gibbs free energy) of activation with respective values of – 0.205 kJ/mol.K, 15.34 kJ/mol, and 83.54 kJ/mol, confirming the endergonic, endothermic, and non-spontaneous nature of the reaction. Thus, the determination of key process conditions with the kinetic and thermodynamic properties of the KSSO esterification process could aid the use of the oil as a viable feedstock for biodiesel synthesis and reactor design for industrial applications. • High free fatty acid Khaya oil was esterified with methanol to < 1%. • Ferric sulfate served as a solid heterogeneous acid catalyst for the esterification. • Minimum %FFA of 0.49 was obtained with the optimum values predicted by the model. • The esterification process followed pseudo first-order kinetics. • The nature of the reaction was endergonic, endothermic, and non-spontaneous.