Abstract
This study evaluates the integrated valorization of solid residue from a biorefinery process, focusing on the production and comparison of briquettes from raw and diluted sulfuric acid-pretreated lignocellulosic residues: Banana Pseudostem (BPS), Guava Seed Cake (GSC), and Urban Tree Pruning (UTP). The pretreatment, conducted at 140 °C, 40 min, and 3.5% sulfuric acid (H 2 SO 4 w/v), solubilized all hemicellulose content, resulting in a solid fraction enriched in cellulose and lignin. The briquettes were manufactured under fixed parameters (90 °C, 10 MPa, 3 min (residence time), and 7 min (cooling period), demonstrating good durability (greater than 98.7%) and minimal volumetric expansion in all samples. Critically, the pretreated materials produced superior fuel quality, exhibiting improved apparent density, energy density, and High Heating Value (HHV) due to chemical conditioning. Combustion tests further validated this, showing that the pretreated briquettes exhibited slower mass degradation and maintained high temperatures longer than the feedstocks. Among all biomasses, GSC residues stood out, notably achieving the highest HHV (approximately 21.6 MJ/kg) and exhibiting an anomalous increase in mechanical strength post-pretreatment, attributed to the synergistic binding effect of enriched lignin and residual oils/proteins. These findings affirm that dilute acid pretreatment not only enables the production of fermentable sugar (liquid phase) but also simultaneously transforms the solid residue into a superior feedstock for solid biofuels, successfully closing the circular economy loop for various lignocellulosic residues.