Esterification of oleic acid using Zn-Cu/HZSM-5 and design of a fixed bed reactor for biodiesel production

Microwave-assisted esterification of oleic acid (OA) with methanol (MeOH) was investigated using a Zn-Cu/HZSM-5 bimetallic heterogeneous catalyst as a rapid and potentially energy-efficient route for biodiesel production. The catalytic performance was compared with homogeneous H 2 SO 4 under conventional and microwave-assisted conditions. The effects of reaction temperature, OA:MeOH molar ratio, catalyst loading, reaction time, and microwave power were systematically evaluated. Under the optimized conditions of 70 °C, an OA:MeOH molar ratio of 1:8, 0.5 g catalyst loading, 40 min reaction time, and 300 W microwave power, 90% OA conversion and 86% methyl oleate selectivity were achieved. Compared with conventional reflux, which required approximately 24 h, microwave irradiation substantially shortened the reaction time. The enhanced catalytic performance is attributed to the synergistic interaction between Zn and Cu species, which modifies the surface acidity of HZSM-5 and promotes reactant activation, combined with efficient microwave dielectric heating. The novelty of this work lies in integrating Zn-Cu bimetallic HZSM-5 catalysis with microwave-assisted oleic acid esterification under mild operating conditions, together with systematic process optimization and kinetic evaluation for potential scale-up. Based on the developed kinetic model, a fixed-bed reactor configuration is proposed for continuous operation, with feed flow rate and reactant concentration identified as key parameters for further scale-up studies. Overall, the findings demonstrate the potential of Zn-Cu/HZSM-5 combined with microwave heating as a rapid and more sustainable approach for fatty-acid esterification and biodiesel production.