Investigation on the Impact of Coexisting Component for the Catalytic Hydrogenolysis of Cellulose in Bagasse to 2,5-Hexanedione

Catalytic conversion of cellulose in biomass into 2,5-hexanedione is a significant step for the production of biobased p-xylene (PX), and a precise understanding about the effect of the coexisting hemicellulose and lignin components is extremely essential and desirable, but still severely deficient. Herein, we investigate the above issue by catalytic tests, structural characterizations, and composition analysis. Catalytic tests confirm that the coexisting hemicellulose does not affect cellulose conversion and could be converted into 5-chloro-2-pentanone, while the lignin component plays a detrimental role. Lignin and the oligomers from lignin hydrogenolysis can block the catalytic active sites via deposition due to the strong interaction between lignin and Pd/C catalyst. Meanwhile, there is noncovalent interaction between lignin and cellulose, reducing the accessibility of cellulose to the catalytic active sites including the Pd/C and acidic sites. Basic treatment by NaOH aqueous solution could result in simultaneous removal of lignin and fracture of the biomass structure and hence higher accessibility for the Pd/C catalyst. When the biomass is treated by NaOH with the concentration of 1.0 wt %, the amount of lignin (8.3 wt %) is low enough and the structure is fractured enough to achieve the yield of HDO and DMF comparable to that using sole cellulose as the reactant.