Microalgae are an alternative source for biodiesel production, because they have more advantages than crop plants, i.e. high lipid content, can grow in freshwater or saltwater, faster growth rate and high productivity. In this context, our research was focused on the production of microalgae biomass from Scenedesmus opoliensis grown in mixotrophic conditions with glycerol as cheap carbon source and valorization of extracted algal oil as biodiesel. However, the extracted oil has high free fatty acids (FFA) and requires pre-treatment, if homogeneous catalysts are used due to saponification phenomenon and post-production processes. To avoid this inconvenience, the biodiesel was obtained in two steps: esterification of FFA with methanol over amphiphilic SO42-/TiO2-ZrO2 superacid catalyst and transesterification over KOH.
The amphiphilic superacid catalyst was prepared by surface modification of SO4/TiO2-ZrO2 withn-octadecyltrichlorosilane and characterized using X-ray diffraction, TGA analysis, FT-IR spectroscopy and BET analysis. The FT-IR and TGA analysis confirm the attachment of alkylsilane on the surface of SO42-/TiO2-ZrO2 support.
The effect of various reaction parameters such as algal oil/alcohol molar ratio, catalyst amount and reaction time on catalytic performance was studied. The acid esterification was carried out to reduce algae oil acidity from 29 % to less than 1 %. After this step, the yield of biodiesel after transesterification with KOH was over 96 %. To improve biodiesel pour point property two glycerol derivatives previous synthesized were blended with algal biodiesel. The results indicated an improvement of tested properties.