(729h) Production of Levoglucosenone from the Catalytic Dehydration of Cellulose and Levoglucosan Using Low Concentrations of Sulfuric Acid in ?-Valerolactone

Levoglucosenone (LGO) is a high value anhydrosugar commonly produced from the pyrolysis of cellulose in low yields. LGO is used in the synthesis of pharmaceutics such as antibiotics, renewable solvents, and other specialty and high value chemicals. Recently, our group studied the production of LGO from cellulose in a batch reactor using low concentrations of a combination of solid and liquid Brønsted acid catalysts in tetrahydrofuran (THF) at high temperature (483 K). We found LGO yields close to those obtained with higher concentrations of liquid acid catalysts. Moreover, the accumulation of water during the dehydration reaction for the production of LGO has a negative effect in the LGO yields. The water produced appears to stabilize the acid protons (H⁺) decreasing its reactivity. Trying to decrease the effect of water and avoiding the volatility of THF, we studied the dehydration of cellulose to LGO using a flow reactor and low concentration of H₂SO₄ as catalyst in γ-valerolactone (GVL) as solvent. GVL is polar aprotic biomass derived solvent with properties similar to THF but less volatile than THF. We obtained LGO yields up to 30% and yields towards levoglucosan (LGA) up to 35% using a temperature of 430 K and 5mM H₂SO₄. An increase in temperature increases the yields towards undesirable products such as 5-hydroxymethylfurfural (HMF) and formic acid decreasing the LGO yields. We also studied the kinetics of the dehydration of LGA to LGO in GVL using a batch reactor system at atmospheric pressure. We found LGO selectivities up to 43% using a temperature of 430 K and 5 mM H₂SO₄ in GVL. Reactions at a temperature of 383 K and 5 mM H₂SO₄ suggest that LGA reacts to form an intermediate molecule before LGO is produced. This molecule maybe 1,4:3,6 Dianhydro-α-D-glucopyranose (DGP), a molecule identified in the cellulose pyrolysis.