Biochar-based solid acid catalyst enables highly efficient conversion of cellulose to formic acid in DMSO/H2O biphasic system

Formic acid (FA), a versatile platform chemical and hydrogen carrier, faces production challenges from cellulose due to its recalcitrant crystalline structure and reliance on precious metal catalysts. This study demonstrates a sustainable approach using biochar solid acid (BC-PO4), a biochar-phosphoric acid solid acid catalyst derived from coconut husk, for efficient cellulose-to-FA conversion. Machine learning-guided optimization random forest algorithms (RF) with Box-Behnken design (BBD) achieved 60.4 % FA yield with 70.1 % selectivity in 3.8 h under mild conditions:194 °C, 3.2 MPa O2, using 180 μL DMSO (dimethyl sulfoxide) and 0.05 g catalyst. Kinetic modeling and time-gradient experiments revealed that the DMSO/H2O biphasic system significantly enhances cellulose conversion to FA compared to a single H2O solvent system. Life cycle analysis (LCA) showed the BC-PO4 process generates 23–35 % lower CO2-equivalent emissions than H2SO4 or HNO3-derived catalysts. The techno-economic assessment confirmed feasibility with an operational cost of 11.9 $/kg FA. This catalytic system addresses three critical barriers: (1) replacement of noble metal catalysts with biomass-derived alternatives, (2) reduction of process severity through solvent engineering, and (3) improved sustainability metrics compared to mineral acid-based systems. The integration of agricultural waste upcycling, green catalyst design, and AI-assisted process optimization establishes a scalable pathway for biomass valorization to high-value chemicals.