Thermogravimetric kinetic analysis of mallow (Urena lobata Linn.) stem residues to evaluate their potential in energy applications

The growing demand for renewable energy has increased interest in the use of lignocellulosic residues for energy applications. Mallow (Urena lobata Linn.) stem residue is an underutilized Amazonian byproduct generated after fiber extraction, whose thermal degradation behavior remains poorly explored. This study evaluated the energy-related potential of mallow stem residue through thermogravimetric analysis, TG-MS, isoconversional kinetic modeling, thermodynamic assessment, and reaction mechanism analysis. The biomass was characterized by proximate and lignocellulosic analyses and subjected to non-isothermal thermogravimetric experiments under N 2 atmosphere at heating rates of 2.5, 5, 10, 15, and 20 °C min -1 . The use of FWO, Kissinger-Akahira-Sunose, Starink, and Vyazovkin methods allowed the consistency of activation energy estimates to be evaluated and enabled the conversion-dependent reactivity of the biomass to be described without assuming a single reaction model. TG/DTG results revealed a multistage degradation process, with the main devolatilization occurring between 200°C and 400 °C. TG-MS indicated the release of H 2 O, CO 2 , and light organic fragments, while minor m/z assignments were treated as tentative due to possible fragment overlap. The apparent activation energy decreased with conversion, ranging from approximately 133 to 104 kJ mol -1 , with average values between 122.95 and 126.39 kJ mol -1 . Thermodynamic parameters indicated a thermally activated and energy-demanding decomposition process, while reaction mechanism analysis suggested changes in the dominant mechanism throughout conversion. Overall, mallow stem residue showed thermal and kinetic characteristics comparable to other lignocellulosic feedstocks, indicating potential for energy-related applications. However, further product characterization, ash composition analysis, and reactor-scale studies are required to confirm its practical applicability in bioenergy conversion systems.