Microwave-Assisted Transesterification of Argemone mexicana Oil: Parametric and Kinetics Study

Abstract

Argemone mexicana is one of the high non-edible oil plants easily grown in barren land. The current study employs microwave-assisted transesterification of Argemone mexicana oil (AO) into value-added biodiesel. A systematic experimental approach was utilized to investigate the effect of methanol-to-oil molar ratio, catalyst amount, reaction temperature and time on free fatty acid conversion and Argemone mexicana oil methyl ester (AOME) at constant stirring using microwave power. Response trends suggested that the biodiesel yield was maximized to 96% with increasing time, molar ratio, catalyst amount, and temperature up to an optimum value of 3 min, 9:1 methanol-to-oil molar ratio, 1% NaOH, and 60 °C, respectively. Beyond these conditions equilibrium limitations and possible reverse reactions led to reduced yield. FTIR was employed to do a qualitative investigation of AO and AOME. The emergence of a new signal at 1435 cm⁻¹ confirmed the development of AOME. The ¹H-NMR research found that 94.91% of the oil was converted into biodiesel. The kinetics of AO transesterification were first-order, with a rate constant 0.726 min⁻¹ at 60 °C and an activation energy 27.49 kJ mol⁻¹. The non-thermal impact of the microwave was also revealed by the high frequency factor 14871 min⁻¹. At 60 °C, the changes in Gibbs free energy, enthalpy and entropy were 94.09 kJ mol⁻¹, 24.734 kJ mol⁻¹ and −0.2083 kJ mol⁻¹ K⁻¹, respectively. The thermodynamic study revealed that it was an endergonic and non-spontaneous process.