(102a) In-Flow Production of Levoglucosenone from the Catalytic Dehydration or Cellulose Using Homogeneous Brønsted Acid Catalysts in ?-Valerolactone

Levoglucosenone (LGO) is an anhydro-sugar used in the organic synthesis of high value pharmaceutics (e.g., antibiotics and anticancer drugs); renewable solvents such as Cyrene®; 1-6-hexanediol used to produce polymers; and other specialty and high value chemicals [1]. Recently, our research group in collaboration with George Huber’s at the University of Wisconsin – Madison studied the production of LGO from cellulose in a batch reactor at 483K using low concentrations of acid catalysts in THF. The study showed that similar LGO yields to those obtained with high concentrations of sulfuric acid [1] may be obtained using low concentrations of sulfuric acid and a solid acid catalyst. The study also showed that the water accumulation during the reaction limits the production of LGO. However, at those temperatures THF is flammable and high pressures are needed to keep it in the liquid phase. Here, we studied the catalytic conversion of cellulose to levoglucosenone in a flow reactor using homogenous Brønsted acid catalysts in a polar aprotic solvent. The flow reactor helps to minimize the concentration of water in the reaction. We used γ–valerolactone (GVL) as solvent because has similar properties to those of THF but it is safer. We demonstrated that using a flow-through reaction system and low concentrations of Brønsted acid catalysts such as sulfuric acid (H₂SO₄), phosphoric acid (H₃PO₄) or 1-propanesulfonic acid in GVL as solvent, high yields of LGO from cellulose are obtained. For GVL, the yield towards LGO passes through a maximum as a function of the reaction temperature at 445K. Thermal pretreatment of the cellulose at 455 K before the reaction decreases the yield to LGO. An increase in the catalyst concentration does not significantly increase the yield towards LGO, but decreases the yield towards LGA. We studied the effect on the LGO yield of the catalyst type, the cellulose loading and the crystallinity of the cellulose. Using a reaction temperature of 445K and 5mM of H₂SO₄ as catalyst, the total carbon and LGO yields were 81% and 65%, respectively. To our knowledge this LGO yield is the highest yield for cellulose conversion reported so far.

[1] F. Cao, T. J. Schwartz, D. J. McClelland, S. H. Krishna, J. A. Dumesic, and G. W. Huber, “Dehydration of cellulose to levoglucosenone using polar aprotic solvents,” Energy Environ. Sci., vol. 8, no. 6, pp. 1808–1815, 2015.