Synergistic Effect of Different Species in Stannic Chloride Solution on the Production of Levulinic Acid from Biomass

Metal chloride has shown high potential in biomass conversion to valuable chemicals, but the nature of active species and the corresponding performances on each successive reaction step need further elucidation. In this work, SnCl4 was found to exhibit satisfactory catalytic activity, achieving 64.6 mol % yield of levulinic acid from corncob residue. The levulinic acid obtained could be further converted to more valuable ethyl levulinate with 85% yield without any extra catalyst addition. In water medium, the hydrolysis of SnCl, resulted in the formation of stannic oxide, H+ and Cl-, which showed a synergistic effect and all contributed to levulinic acid production. It was demystified that Cl- promoted cellulose hydrolysis, and the formed H+ as Bronsted acid mainly contributed to cellulose hydrolysis and fructose dehydration, as well as HMF decomposition to levulinic acid. Sn(IV) species facilitated both glucose-to-fructose isomerization and fructose consumption yielding undesirable polymers, but exhibited a negative influence on cellulose hydrolysis. The proposed kinetic model showed a good fit with the experimental result, and further confirmed the proposed catalytic mechanism. The insights reported here might give some useful information for the development of effective catalysts to produce valuable chemicals directly from raw lignocelluloses.