Integrated feedstock chemistry and prepared-microstructure controls on inert decomposition of briquetted biomass residues: Groundnut shell versus pine wood chippings

Feedstock variability remains a major constraint in small-scale biomass conversion systems, yet preliminary feedstock screening often relies on bulk fuel properties that provide limited insight into decomposition behavior. This study compares binder-less briquetted groundnut shell (GNS) and pine wood chippings (PWC) to determine how bulk composition, prepared-surface morphology, surface elemental signals, and broad functional-group signatures coincide with inert thermal decomposition behavior. Both feedstocks were conditioned to low moisture content and characterized using proximate analysis, higher heating value determination, thermogravimetric analysis under nitrogen, SEM-EDX, and ATR-FTIR. PWC exhibited higher volatile matter than GNS (71.88 vs. 67.40 wt% db.) and lower ash content (1.72 vs. 3.30 wt% db.), whereas GNS showed higher fixed carbon (19.94 vs. 17.18 wt% db.) and higher HHV (18.87 vs. 17.04 MJ kg⁻¹). Under inert heating, PWC decomposed earlier, with lower onset and peak decomposition temperatures, whereas GNS retained substantially more terminal residue at 1000 °C. SEM revealed a more heterogeneous, fracture-dominated prepared surface for GNS and a more fibrous, channel-like prepared surface for PWC. EDX and ATR-FTIR further supported differences in detected surface elemental balance and broad functional-group profiles. Overall, the results demonstrate statistically consistent differences between the two briquetted residues and establish a characterization-based basis for cautious preliminary screening. In the absence of ultimate analysis, direct lignocellulosic fractionation, mineralogical analysis, and reactor-scale gasification testing, the findings define a comparative laboratory basis for interpreting inert decomposition behavior, rather than a predictive framework for gasifier performance.