Application of Box-Behnken design in optimization of biodiesel yield using WO3/graphene quantum dot (GQD) system and its kinetics analysis

Abstract

In the current research, we report on the synthesis of WO3/GQD system as a heterogeneous catalyst for the transesterification of waste cooking oil into biodiesel using methanol. The characterization of the prepared catalyst was done by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscope (TEM), energy-dispersive X-ray (EDX), Fourier transform-infrared spectroscopy (FT-IR) techniques, and Brunauer-Emmett-Teller surface area measurement. To study the effect of process variables such as methanol to oil ratio, reaction temperature, and time, we have employed response surface methodology (RSM) based on Box-Behnken design (BBD). The suitability of the predicted model was verified, and the average biodiesel yield of (96.8 ± 0.16%) was reported at optimal reaction condition of 1:6 oil to methanol ratio, 70 °C reaction temperature, 2 wt% catalyst loading, and 3.5 h reaction time. Biodiesel was characterized using proton nuclear magnetic resonance (1H NMR) and carbon nuclear magnetic resonance (13C NMR) techniques, and fatty acid methyl ester composition was determined using gas chromatography-mass spectrometry (GC-MS). Fuel properties of the biodiesel obtained comply with ASTMD6751 biodiesel standards. The kinetics of transesterification was studied and found to follow pseudo-first order. The results showed the rate constant ranging from 0.0028 to 0.007 min−1, activation energy (Ea) of 55.92 kJ mol−1, and frequency factor (A) of 1.72 × 106 min−1.