Synthesis and characterization of ZnO nanoparticles for the production of biodiesel by transesterification: Kinetic and thermodynamic studies

Under sol–gel conditions, a stable zinc oxide powder with nanoparticle morphology was synthesized utilizing zinc nitrate as a precursor, EDTA as a complexing agent, and citric acid as a stabilizing agent. Zinc oxide nanoparticles were characterized utilizing XRD, SEM, BET, EDXRF, FT-IR, and UV–Vis techniques. The catalytic activity of the ZnO nanoparticle catalyst was successfully evaluated by carrying out a transesterification reaction in sunflower oil (SFO). To establish the optimal conditions for biodiesel synthesis, the transesterification process was carried out under various reaction parameters. Several oil-to-metal ratios (1:10, 1:20, and 1:30) were investigated at various times ranging from 1 to 4 h in a reaction operated at temperatures of 60, 65, and 70 °C. The results indicate that ZnO catalysts show good performance in biodiesel production from sunflower oil and provide a biodiesel yield of 71%. under optimal reaction conditions, i.e., methanol to oil molar ratio of 20:1, catalyst amount of 4.7 wt%, and a reaction temperature of 70 °C for 3 h. The catalytic activity can be attributed to the existence of an optimal number of catalytically active sites on the surface of the catalyst. The composition analysis of the synthesized biodiesel was studied using different characterization techniques, such as GC–MS and FT-IR, to identify the FAMEs. The kinetics of the transesterification reaction indicate a pseudo-first-order reaction, and the rate of the reaction is calculated. Thermodynamic functions such as activation energy, heat content, entropy, and Gibbs free energy were determined. The physical and chemical properties of synthetic biodiesel, such as density, viscosity, flash point, pour point, acid value, and water content, were studied and compared against international standards.