Abstract
Biodiesel production offers a promising route towards the achievement of net-zero emissions by 2050. However, current reliance on unsustainable feedstocks and inefficient processes hampers its commercial viability. This study investigates the transesterification of waste cooking oil (WCO) with methanol in a continuous microreactor (1 mm internal diameter) and systematically compares pseudo-homogeneous and biphasic second-order kinetic models for describing the reaction. The biphasic model provided the highest predictive accuracy by explicitly accounting for interfacial mass transfer and phase interactions, whereas the pseudo-homogeneous model offered a simpler formulation with comparable overall statistical performance when model complexity was considered. The activation energy estimated using the biphasic model was 15.61 kJ mol−1, which is lower than values typically reported for homogeneous base-catalysed systems, which is consistent with the enhanced mass-transfer characteristics of the microreactor. Thermodynamic activation parameters were also determined, resulting in an activation enthalpy of 12.93 kJ mol−1, an activation entropy of −272.3 J mol−1 K−1 and an activation free energy of 94.08 kJ mol−1, indicating an energetic barrier to the formation of the activated complex and a more ordered transition state than the reactants. The results demonstrate that explicit treatment of phase interactions improves kinetic prediction while providing practical guidance for selecting kinetic models according to the intended engineering application. These findings support the use of intensified microreactor systems and physically representative kinetic models for the design and scale-up of sustainable biodiesel production processes.