Sequential organosolv fractionation/hydrolysis of sugarcane bagasse: The coupling use of heterogeneous H₃PO₄-activated carbon as acid promoter and hydrolysis catalyst

Separation of lignocellulose constituents and hydrolysis of the polysaccharides fraction to sugars are pre-requites in production of biofuels and chemicals. In this study, a sequential organosolv fractionation of sugarcane bagasse and saccharification of the cellulose-enriched pulp in hot compressed water using a coupled heterogenous acid promoter/catalyst was studied. Among the liquid and solid acids tested, H₃PO₄-Activated carbon showed a high performance on promoting selectivity and yield in fractionation related to its high BET surface area and acid site density. Fractionation in a ternary mixture of methyl isolbutylketone:methanol:water (16:68:16) at 180 °C for 60 min using 5%w/w H₃PO₄-Activated carbon resulted in 88.9% recovery of cellulose enriched in the solid, together with 84.6% recovery of the hemicellulose as pentoses in the aqueous-alcohol fraction and 76.0% lignin in the organic phase. With no separation of the solid acid, the cellulose fraction could be further hydrolyzed under hot compressed water conditions at 225 °C for 10 min, resulting in the maximal hexose yield of 58.3% from the starting material. The catalyst retained >80% activity after reusing in five consecutive batch cycles. The work demonstrates an efficient integrated fractionation/hydrolysis process with coupling use of the acid promoter/catalyst, with advantages on its high activity, selectivity and reusability.