Comprehensive Physicochemical Characterization and Pyrolysis Kinetics of Halfa Grass ( Desmostachya bipinnata ) for Sustainable Bioenergy Applications

Abstract

ABSTRACT Halfa grass ( Desmostachya bipinnata ) is an abundant lignocellulosic biomass with potential for thermochemical conversion and biochar production. This study investigated its physicochemical characteristics, pyrolysis kinetics, reaction mechanism, and thermodynamic behavior using an integrated experimental approach. Elemental analysis, Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to characterize the biomass and the derived biochar. Thermogravimetric analysis (TGA) was conducted under a nitrogen atmosphere at heating rates of 10, 20, and 30°C min − 1 . The TG–DTG profiles revealed a typical multi‐stage decomposition pattern associated with the degradation of hemicellulose, cellulose, and lignin fractions. The activation energy was determined using Flynn–Wall–Ozawa (FWO), Friedman (FM), Kissinger, and Vyazovkin (VYZ) methods. The average activation energies obtained from the FWO, FM, VYZ, and Kissinger methods were 144.28, 151.09, 150.79, and 156.00 kJ mol − 1 , respectively, demonstrating good agreement among the applied kinetic approaches. The variation of activation energy with conversion confirmed that halfa grass pyrolysis proceeds through multiple overlapping reactions rather than a single elementary process. Master plot analysis indicated that diffusion‐related models provided the closest agreement with the experimental data over different conversion ranges, although additional validation would be required for definitive mechanistic confirmation. Thermodynamic analysis revealed positive enthalpy and Gibbs free energy values, indicating that the decomposition process is endothermic and requires continuous energy input. FTIR and XRD analyses demonstrated substantial structural transformation during pyrolysis, including the decomposition of oxygen‐containing functionalities and the formation of condensed aromatic carbon structures within the resulting biochar. These results provide valuable insight into the thermal decomposition behavior of D. bipinnata and contribute to a better understanding of its physicochemical and kinetic characteristics for future thermochemical conversion and biomass valorization applications.