Optimization of biodiesel production from waste cooking oil by magnesium oxide nanocatalyst synthesized using coprecipitation method

Nanostructured magnesium oxide (MgO) catalysts were prepared by the coprecipitation method and employed for the transesterification of waste cooking oil using methanol. The X-ray diffraction analysis showed that nanostructured MgO phase was formed at calcination temperature of 500 °C. The mean crystallite size of MgO nanoparticles is 7.86 nm. Fourier-transformed infrared spectroscopy studies confirmed the formation of MgO phase with the characteristic vibrational mode of Mg–O. UV–Vis diffuse reflectance spectroscopy reveals that the energy band gap is around 5.84 eV. The presence of magnesium and oxygen elements was determined from energy-dispersive X-ray analysis. The effect of various parameters such as catalyst loading, methanol-to-oil molar ratio, reaction temperature, reaction time and reusability was investigated. A maximum biodiesel yield of 93.3% was achieved with 2 wt% of MgO nanocatalyst (MO5 sample), methanol/oil molar ratio of 24:1, reaction temperature about 65 °C and reaction time 1 h. The nanocatalyst (MgO) was reused at least for 5 times and thereafter resulted in a decrease in the biodiesel yield. The kinetic study of the transesterification reaction followed pseudo-first-order rate kinetics. The composition of fatty acid methyl ester was determined using gas chromatography–mass spectroscopy.