Sunday, May 3, 2009
3-87
Kinetic modeling of glucose reversion reactions
H.M. Pilath, M.E. Himmel, M.R. Nimlos, and D.K. Johnson. National Renewable Energy Laboratory, Golden, CO 80401
In this study, we have directly measured glucose reversion reactions and have extracted the kinetics of formation of glucose dimers through modeling. While dehydration reactions are well known acid-catalyzed reactions leading to loss of sugar and the formation of potential fermentation inhibitors, reversion reactions (those that lead to the formation of oligosaccharides) have received much less attention, even though these reactions can account for a significant loss of sugars (up to 12% glucose, 9% xylose). Our goal has been to develop a complete picture of the mechanism of reversion reactions using glucose so as to help elucidate the reversion reactions of xylose which are directly relevant to biomass pretreatment. Identification of individual dimers from xylose reversion reactions is difficult due to a lack of standards, so we have modeled the kinetics of dimer formation using the reversion reactions of glucose.
Reversion reactions of glucose to all possible dimers have been measured as have the kinetics of hydrolysis of several of these dimers. These measurements were made in mildly acidic aqueous solutions that were heated using microwave radiation. From these experiments, we determined the kinetics of the reactions, their activation energies and the equilibrium constants for the reversion reactions by modeling all of the products formed. Included in this model is anhydrosugar formation (i.e., levoglucosan) from glucose. In addition, we discuss concentration effects (acid as well as sugar concentration). The ultimate goal is to develop quantitative kinetic parameters that can be used to design and optimize biomass pretreatment reactors.