Biodiesel production from waste frying oil using molybdenum over niobia as heterogeneous acid catalyst: Process optimization and kinetics study

Abstract

In this study, a new acid solid catalyst composed of MoO3 impregnated in Nb2O5 was synthesized and applied in methylic transesterification reaction of Waste Frying Oil (WFO) for biodiesel production. The catalyst was synthesized by the wet impregnation method and characterized by Surface Acidity, X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Energy Dispersion X-Ray Spectroscopy (EDS). The transesterification reaction variables were studied using the One Variable at Time (OVAT) technique at the following intervals: temperature (100–160 °C), reaction time (1–3 h), methanol:oil molar ratio (10:1–30:1) and catalyst loading (2–10 wt%). From the results of the catalytic tests, a maximum conversion value of 94.2% was obtained for esters in the following optimized reaction conditions: 145 °C temperature, 2.5 h reaction time, 20:1 methanol:oil molar ratio and 6 wt% catalyst loading. The catalyst was recovered and showed high reusability and stability over eight reaction cycles, with ester content above 80% after seven cycles. Through the kinetic study the activation energy (Ea) and the thermodynamic parameters ΔH#, ΔS# and ΔG# were evaluated following a pseudo first order reaction and their values were 32.00 kJ mol−1, 28.66 kJ mol−1, -0.21 kJ mol−1 K−1 and 118.02 kJ mol−1, respectively.