Biodiesel Production from Microalgal Oil Using Barium-Calcium-Zinc Mixed Oxide Base Catalyst: Optimization and Kinetic Studies

Spirulina platensis was cultivated in a vertically aligned photobioreactor for biodiesel synthesis. The algal culture was harvested by centrifugation, and the biomass was dried in an oven. The oil was extracted by solvothermal techniques in a microwave at 60 degrees C for 30 min and 750 W. The mixed metal oxide (barium-calcium-zinc) heterogeneous catalyst was synthesized and used in biodiesel synthesis from Spirulina oil. The synthesized catalyst was characterized by using sophisticated techniques, viz thermogravimetric analysis-differential scanning calorimetry, powder X-ray diffraction, attenuated total reflectance-Fourier infrared spectra, scanning electron microscop-energy-dispersive X-ray spectroscopy, and surface area analyzer. The optimization study was performed on several reaction parameters, such as temperature, time, molar ratio, catalyst weight, and stirring speed. The maximum fatty acid methyl esters conversion was found to be 98.94% at optimized parameters of 2.5 wt % catalyst, 1:18 molar ratio (methanol/oil), 600 rpm stirring speed, and 65 degrees C temperature for 120 min. Reusability of the catalyst was monitored, and it was found to be reusable for six cycles with 69.56%. The basic site of the catalyst was a function of catalyst activity, which relies on the barium content. Kinetic parameters have been evaluated by applying pseudo first-order kinetic equation for transesterification of Spirulina oil. The activation energy (E-a) for the catalyzed transesterification reaction was found to be 48.02 kJ mol(-1).