Integrated biorefinery of cacao biomass: catalytic lignin valorization and production of phenolic-bio-oil using Ni-NiO/α-Al₂O₃

In countries where large-scale crops are grown, lignin-rich residual biomass is a problem due to its accumulation and its tendency to attract pests, but it is also a material with potential for valorization. Agricultural residues from cocoa represent an abundant source of lignocellulosic biomass with high potential for valorization within biorefinery processes. In this study, a lignin-first catalytic fractionation approach was applied to cocoa pod biomass using a Ni-NiO/α-Al2O3 catalyst and isopropanol as solvent, which acts as an in-situ hydrogen donor. The process aimed to promote the selective depolymerization of lignin while valorizing the carbohydrate fraction. The catalytic system favored the formation of lignin-derived phenolic compounds, achieving a maximum of 436.8 μg/mL of total phenols (220 °C, 180 min, 80% alcohol). Guaiacol was identified as the main product, suggesting a lignin structure rich in guaiacyl units. Physicochemical characterization (BET, TGA, SEM) revealed structural modifications in the treated biomass, including increased surface area and porosity. Acid hydrolysis showed that under severe conditions (120 °C, 150 min), raw biomass produced high concentrations of glucose (2744.11 mg/L) and fructose (3192.32 mg/L), whereas treated biomass released only 154.73 mg/L of fructose. Under milder conditions (70 °C, 20 min), the treated biomass exhibited improved glucose release compared to raw biomass, indicating enhanced accessibility of residual polysaccharides. Overall, the results demonstrate that the catalytic fractionation of cocoa biomass enables the valorization of the lignin fraction into valuable phenolic compounds while simultaneously modifying the structural properties of the residual solid.