Estudo integrado da macaúba (Acrocomia aculeata): caracterização físico-química, pirólise termogravimétrica lenta e de determinação da energia de ativação por métodos isoconversionais

Abstract

The continuous use of fossil fuels, the growing concern with global warming, and environmental pollution have driven the search for renewable energy sources and alternative technologies. In this context, the use of lignocellulosic biomass, such as macaúba (Acrocomia aculeata), has stood out as a promising renewable raw material to produce bioenergy and biofuels through thermochemical conversion. This study investigated the fractions of macaúba (epicarp, mesocarp, endocarp, and almond cake) through physicochemical analyses and, by means of thermogravimetric pyrolysis, the reaction kinetics. Proximate and ultimate analyses indicated that the mesocarp has the highest volatile content (87%) and a higher heating value (HHV) of 22 MJ/kg, being the most promising fraction for slow pyrolysis. FTIR analyses confirmed the predominant presence of cellulose, hemicellulose, and lignin. Thermogravimetric analyses were carried out in an inert atmosphere with heating rates of 5, 10, 15, and 20 °C/min, showing that mesocarp and epicarp decompose rapidly between 250 and 400 °C, while endocarp and almond press cake present slower degradation, up to 600 °C. With the pyrolysis kinetics, the activation energy (Ea) was calculated using the isoconversional methods of Friedman (FR), Kissinger-Akahira-Sunose (KAS), and Flynn-Wall-Ozawa (FWO), presenting average values of 186 to 202 kJ/mol for the mesocarp and 232 to 235 kJ/mol for the endocarp. Under oxidative atmosphere, the almond press cake reached Ea values up to 342 kJ/mol. The results validated the potential of macaúba for energy applications with integrated residue utilization, with epicarp and mesocarp indicated to produce bio-oil and endocarp and almond press cake to produce biochar.