Extração de lipídios da microalga poterioochromonas malhamensis, visando à produção de biodiesel pela reação de transesterificação in situ

Abstract

Due to population growth and rapid industrialization, there has been a significant increase in the use of petroleum derivatives. Alongside the rapid adoption of fossil fuels, there has also been a heightened awareness of the environmental impacts they generate, such as global warming and acid rain. In addition to environmental concerns, these fuels are finite and projected to deplete. Thus, the quest for alternative energy sources is paramount. In this context, regardless of the alternative adopted, it is crucial to increase the contribution of renewable and environmentally friendly sources, with biodiesel standing out. The search for new raw materials for biodiesel production has been prominent in recent years, with microalgae considered potentially useful for this process. These photosynthetic microorganisms utilize solar energy, along with water and carbon dioxide, to produce biomass capable of being converted into available energies, such as biodiesel. Consequently, the cultivation of microalgae of the species Poterioochromonas malhamensis was studied in a modified M-8 medium, with cultures conducted both with and without micronutrient supplementation in a 10 L flat-plate reactor at a carbon dioxide flow rate of 8%. The quantities of chlorophyll a and b, as well as carotenoids, were quantified using UV-VIS methods with methanol as the solvent. Various techniques with different solvents were tested for the extraction of crude lipids. Subsequently, a Box-Behnken experimental design, encompassing three levels and three factors (temperature, catalyst quantity, and solvent), was employed to maximize the yield of biodiesel and fatty acids from the resultant dry biomass obtained from the cultivation process. As a result, an ultra-high-density culture was achieved, with approximately 17.50 gL-1 of biomass, 191.837 µg mL-1 of chlorophyll a, 230.285 µg mL-1 of chlorophyll b, and 34.938 µg mL-1 of carotenoids with micronutrient supplementation. The lipid yield obtained the best result using the soxhlet technique, with 12.642 g of lipids per g of biomass. However, the utilization of supercritical fluid extraction yielded better results in terms of ester composition, with a higher quantity of saturated acids. In the in situ transesterification process, there was a slight difference in yield when using methanol and ethanol as solvents. Still, methanol achieved the highest yield in terms of FAME (fatty acid methyl esters) at 65°C for 240 minutes, with 5.8 g of esters per g of dry biomass. In the experimental design for biodiesel production, the optimum parameters were found to be 90°C, 0.45 mL of HCl, and 0.25 mL of methanol solvent, yielding 22 g of biodiesel per g of dry biomass. However, for the experimental design targeting FAME, the central points were identified as the optimal values for catalyst, solvent volume, and temperature (0.25 mL, 2.5 mL, and 65°C, respectively).