Enhanced Biodiesel Production from Botryococcus braunii Using Zn-Doped Eggshell-Based CaO Nanocatalyst

Abstract

Botryococcus braunii is a microalga that is regarded as a potential source of renewable fuel because of its ability to produce large amounts of lipids that can be converted into biodiesel. This study aims to produce biodiesel from B. braunii microalgae oil with methanol using efficient and low-cost heterogeneous Zn-doped eggshell-based CaO nanocatalyst. The B. braunii species were isolated and cultured in a modified CHU-13 medium. The experiment was performed using white fluorescent light (2500 lux) at a photoperiod of 16:8hour light and dark cycle. The microwave assisted solvent extraction method was used to extract microalgae oil. Synthesized nanocatalysts were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) techniques. The results showed that synthesized eggshell-based CaO calcinated at 900 ℃ and impregnated Zn doped CaO exhibited an average crystalline size of 39.12 nm and 44.74nm, respectively with a regular shape, porous in structure by possessing a greater number of active sites. The total lipid content of B. braunii biomass in this study was found to be 37.7%. Taguchi’s experimental design was used for the production of microalgae oil methyl ester using process parameter optimization; four factors (i.e. alcohol to oil molar ratio, catalyst concentration, reaction temperature, and reaction time) were optimized. Signal/noise (S/N) ratio and analysis of variances (ANOVA) were employed to find out the optimal process parameters. Upon optimization, maximum biodiesel conversion of 96.21% was recorded under the reaction conditions of 16:1 methanol to oil molar ratio, 5 wt% catalyst loading, 50 °C reaction temperature and 120 min of reaction time. Taguchi’s model described the accuracy of the statistical approach for fatty acid methyl esters yield with R-sq: 96.18% and R-sq (adj): 92.37%. The fuel properties of the produced biodiesel were analyzed according to ASTM D6751 standards and were also good in comparison to conventional diesel. The results of this study indicated that B. braunii species is a promising source of feedstock for biodiesel production as an alternative source of fuel via microwave-assisted oil extraction and the use of eggshell-based Zndoped CaO as a nanocatalyst.