Process Analysis, Chemical Characterization and Antioxidant Activity of Açaí (Euterpe oleracea Mart.) Seeds Pyrolysis Bio‐Oil

In this study, the influence of chemical impregnation with an aqueous solution of sodium hydroxide (NaOH) at 1 mol·L⁻¹, combined with temperature variation, was systematically investigated at the laboratory scale on the yield of pyrolysis products (bio-oil, gas, water, and biochar), as well as on the physicochemical properties (acid value, density, and kinematic viscosity), chemical composition (hydrocarbons and oxygenated compounds), and antioxidant properties of the bio-oil obtained from açaí seeds (Euterpe oleracea Mart.). The pyrolysis reactions were carried out at temperatures of 350 °C, 400 °C, and 450 °C under a pressure of 1.0 atmosphere. The NaOH impregnation played a crucial role in modifying the thermal degradation pathway of the biomass, promoting the formation of specific chemical structures and altering the product yields. NaOH acted as a catalyst, favoring the deoxygenation processes of the biomass and enhancing the formation of hydrocarbons. As a result, the yields of bio-oil, water, biochar, and gas ranged from 7.0 to 10.22% (by weight), 28.54 to 29.95% (by weight), 26.44 to 33.63% (by weight), and 25.86 to 34.37% (by weight), respectively, influenced by the increase in temperature. FT-IR analyses indicated the presence of characteristic chemical functions of hydrocarbons (alkanes, alkenes, and aromatics) and oxygenated compounds (phenols, cresols, ketones, esters, carboxylic acids, aldehydes, and furans), with intensification of signals corresponding to hydrocarbons at higher temperatures. GC-MS analysis confirmed hydrocarbons and oxygenated compounds as the main chemical classes present in the bio-oil, showing strong dependence on the pyrolysis temperature. The antioxidant activity was found to be significant, especially at 350 °C, due to the preservation of phenolic compounds. With the increase in temperature, this activity decreases due to the degradation of functional groups. Nevertheless, bio-oil retains residual activity, with potential for antioxidant applications.