Pedro Augusto Arroyo

This work investigates the optimization of in‐situ transesterification of Scenedesmus acuminatus biomass for the synthesis of ethyl esters, emphasizing the effects of temperature, solvent type, reaction time, and agitation on biodiesel yield and composition. The reactions were carried out using ethanol and hydrochloric acid as the catalytic system, with n‐hexane and chloroform as co‐solvents. The influence of each parameter was systematically evaluated to determine optimal conversion conditions. The maximum yield, 78.6 mg ethyl esters g ⁻¹ dry biomass, was obtained at 60°C after 90 min using n‐hexane under static conditions. The effect of agitation was solvent‐dependent. While it did not significantly enhance yields in the n‐hexane system, agitation improved both the final yield and reaction kinetics when chloroform was used as the co‐solvent. Chromatographic analysis revealed that the predominant ethyl esters were C16:0, C16:1, C18:2, and C18:3, indicating a predominance of unsaturated fatty acids. This composition is comparable to that of conventional feedstocks such as soybean and corn oils, suggesting favourable cold‐flow properties but lower oxidative stability. The results demonstrate that ethanol‐based in‐situ transesterification of S. acuminatus provides a sustainable, simplified, and high‐yield route for biodiesel production, reducing process steps and solvent demand relative to conventional extraction methods, reducing process steps by eliminating the need for a separate lipid extraction stage and lowering solvent demand through direct conversion within the biomass, as supported by the high yields achieved with a single reaction mixture and consistent with the efficiencies reported for similar in‐situ systems.

The present work carried out an extensive and deepened study regarding the physicochemical characteristics of two Si-MCM-41-type supports, synthesized employing two distinct silica precursors, tetraethyl orthosilicate (TEOS) and rice husk ash (RHS), with the dispersion of nickel on the surface of the catalytic support. The direct influence of the active phase dispersion was analyzed, making a relationship with the formation of coke and with its performance on methane dry reform (DRM). The catalysts were prepared with 5, 10, and 20% (m/m) of Ni by wet impregnation method (with excess solvent), calcined at 800 ºC for 6 h, and characterized by the techniques of scanning electron microscopy and energy dispersive spectroscopy (SEM/ EDS), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET)/Barret-JoyerHalenda (BJH), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), temperature-programmed ammonia desorption (TPD-NH3), and H2-temperature-programmed reduction (TPR). The DRM experiments were carried out at 800 °C for 24 h with a 1:1 CH4:CO2 molar ratio. Analyzes of gaseous products were performed in gas chromatography (GC) and the coke produced was estimated by temperature-programmed oxidation (TPO). The best reaction results were obtained for catalysts with 20% nickel, which were selective and stable within 24 h of reaction. Comparing the TEOS and RHS catalysts for 20% Ni, the DRM results were very similar. The catalysts on RHS support demonstrated a significant low formation of coke, which can be considered negligible in a 24 h reaction.

The solid waste from urban sewage treatment, such as the sludge that are removed from the drying beds and discharged of biological reactors, are products that need specific treatment, being considered great environmental polluters. These residues can be evaluated from the standpoint of revaluation and, considering the high concentration of lipids that are present in its composition, which can be converted in biodiesel. Thus, the objective of this study was to characterize and evaluate the production of esters by in situ transesterification utilizing the domestic sewage sludge as raw material. The collected sewage sludge presented 61% of organic matter and 39% of fixed solids, with 26% of neutral lipids of the material extracted. High value of the saponifiable material and free fatty acid contend, 22.1% and 97.77 mg KOH/g, respectively, were determined. The potential for biodiesel production was tested and 57.46 ± 2.07 % (m/m) ester yield was obtained with predominance of the unsaturated methyl ester.